The IACOB project: synergies for the Gaia era
S. Simón-Díaz, M. Garcia, A. Herrero, J. Maíz Apellániz, I. Negueruela
aa r X i v : . [ a s t r o - ph . S R ] S e p The IACOB pro ject: synergies for the Gaia era
S. Sim´on-D´ıaz , , M. Garcia , , A. Herrero , , J. Ma´ız Apell´aniz , & I.Negueruela Instituto de Astrof´ısica de Canarias, E-38200 La Laguna, Tenerife, Spain. Departamento de Astrof´ısica, Univ. de La Laguna, E-38205 La Laguna, Tenerife, Spain. Instituto de Astrof´ısica de Andaluc´ıa, CSIC, Apdo. 3004, E-18080 Granada, Spain. Dpto. de F´ısica, Ingenier´ıa de Sistemas y teor´ıa de la Se˜nal. Escuela Polit´ecnica Superior.Univ. Alicante, Apdo. 99, E-03080 Alicante, Spain.
Abstract
The
IACOB spectroscopic survey of Galactic OB stars is an ambitious observational projectaimed at compiling a large, homogeneous, high-resolution database of optical spectra ofmassive stars observable from the Northern hemisphere. The quantitative spectroscopicanalysis of this database, complemented by the invaluable information provided by Gaia(mainly regarding photometry and distances), will represent a major step forward in ourknowledge of the fundamental physical characteristics of Galactic massive stars. In addition,results from this analysis will be of interest for other scientific questions to be investigatedusing Gaia observations. In this contribution we outline the present status of the
IACOBspectroscopic database and indicate briefly some of the synergy links between the IACOBand Gaia scientific projects.
The Gaia mission will gather a complete astrometric, photometric and spectroscopic datasetof over one billion stars. Its instrument performance (see e.g., Prusti, 2011) is designed to pro-vide information about proper motions, radial velocities, photometric variability, distances,interstellar reddening, rotational velocities, atmospheric parameters, and element abundancesof the observed stars. The Gaia observations will hence definitely challenge many aspects ofour present view of the stellar component in the Milky Way.While Gaia photometric and spectroscopic observations will allow a proper character-ization of the stellar properties of late-B and cooler stars (including abundances), a similarstudy in the case of O and early-B type stars will be somewhat limited. On the one hand, theBalmer jump (planned to be observed by the Blue Photometer) is less accurate as indicator
The IACOB project: synergies for the Gaia era
Figure 1:
IACOB-sweg spectra of four representative O stars in the optical (panels A and B) andGaia (panel C) spectral ranges. Contrary to the optical range, the Gaia range is almost empty ofstellar features in the case of O and early B-type stars. Note that the small narrow lines in the Gaiarange (appart from the C ii line) are telluric. of the stellar temperature in this type of stars than in the case of cooler stars. On the otherhand, as illustrated in Figure 1, the spectral range observed by the Radial Velocity Spec-trometer is almost empty of spectral features which could be used to determine rotationalvelocities, and stellar parameters/abundances (contrarily to the optical range). AlthoughGaia observations will allow to distinguish between early/mid-O, late-O, and early-B typestars, a proper (accurate) determination of the stellar parameters will require to combinethese observations with optical spectra (see more details in Section 2.2).Complementing the Gaia database with optical spectroscopic observations of O andearly-B stars is hence of crucial importance for any Gaia scientific project involving stellarparameters and/or abundances of massive stars. Some examples in the context of this con-ference include the full characterization of the IMF of stellar clusters (also accounting for thehigh-mass tail), the study of the impact of massive stars on the formation and dynamicalevolution of young stellar clusters and associations, or the investigation of self-pollution bySNe Type II products in stellar associations with signatures of triggered star formation.Although originally motivated by scientific drivers not directly related to Gaia , large(on going) optical spectroscopic surveys of O and B-type stars such as GOSSS (P.I. Ma´ızApell´aniz), OWN (P.I. Barb´a), NoMaDS (P.I. Pellerin), IACOB (P.I. Sim´on-D´ıaz), andIACOB-sweg (P.I. Negueruela) will become very valuable in the Gaia era. All these surveys,initially independent, are now coordinated and the corresponding spectroscopic databases areplanned to be made public in the future for their maximum exploitation in different scientificcontexts. The GREAT (Gaia Research for European Astronomy Training) networking programme also plans toobserve massive stars in selected clusters as part of more general long term spectroscopic surveys preparingand following Gaia (see Blomme et al., 2011). . Sim´on-D´ıaz et al.
IACOB spectroscopic database and its scientificexploitation, specially remarking some of the synergy links between the IACOB and Gaiascientific projects. Notes on the other surveys can be found elsewhere (e.g. Barb´a et al.,2010; Sota et al., 2011; Ma´ız Apell´aniz et al., 2011).
The
IACOB project (P.I. Sim´on-D´ıaz) aims at progressing in our knowledge of Galactic mas-sive stars using a large, homogeneous, high-quality spectroscopic dataset and modern toolsfor the quantitative spectroscopic analysis of O and B-type stars. The project is dividedinto six main working packages. The first one is devoted to the compilation of the
IACOBspectroscopic database of Northern Galactic OB stars , a very important piece of the project.The other five refer to the scientific exploitation of this unique database of high-resolutionspectra, covering several aspects of interest in the massive star research:
WP-1:
The
IACOB spectroscopic database
WP-4:
Abundances in OB-type stars
WP-2:
Line-broadening in OB stars
WP-5:
Binary/multiple systems
WP-3:
Quantitative spectroscopic analyses
WP-6: massive stars and the ISMThe number of studies planned to be developed in the framework of the IACOB project (i.e.using spectra from the IACOB database) is large. At present, we are concentrating our effortson the investigation of the so-called macroturbulent broadening affecting the line-profiles ofmassive stars and its possible connection to stellar pulsations (e.g. Sim´on-D´ıaz et al., 2010),on the revision of rotational velocities of Galactic OB stars, and on the accurate determi-nation of the stellar and wind parameters of the single O and B stars in the sample. SomeIACOB spectra have also been used to investigate the degree of chemical (in)homogeneityof B-type stars in the Ori OB1 association (Sim´on-D´ıaz, 2010; Nieva & Sim´on-D´ıaz, 2011),or to provide a firm comfirmation of the presence of a third massive star component in the σ Ori AB system (Sim´on-D´ıaz, Caballero & Lorenzo, 2011).Gaia observations will have a definite importance in some of the outcomes of the IACOBproject (mainly regarding WP3). In addition, the analysis of spectra from the IACOBdatabase (in combination with Gaia observations) will provide unvaluable information forother scientific projects studying our Galaxy and/or some of its components. Some examplesof the synergies between IACOB and Gaia will be provided in Sect. 2.2, but first we brieflysummarize the present status and some future prospects of the
IACOB database . The first spectra for the
IACOB spectroscopic database were obtained with the FIES in-strument attached to the Nordic Optical Telescope (NOT) in El Roque de los MuchachosObservatory (La Palma, Spain) in November 2008. Since then, and up to August 2011, wehave compiled ∼ δ ≥ -25 deg. Thepresent version of the database (v2.0) is mainly built on the IACOB v1.0 (Sim´on-D´ıaz et al., The IACOB project: synergies for the Gaia era
IACOB database also counts on a new supplement (
IACOB-sweg , P.I. I. Negueruela). These new observations,obtained with the HERMES spectrograph attached to the Mercator telescope in La Palma,extend further to the red (up to 9000 ˚A) than the FIES spectra. They were planned toinvestigate the spectroscopic behavior of MK standars with spectral types earlier than B9 inthe Gaia range for a optimal future exploitation of the GAIA spectra of this type of stars.
As discussed in Sect. 1, and illustrated in Figure 1 the Gaia spectroscopic observations will beempty of spectral features which could be used to extract information about the fundamentalphysical parameters of OB-type stars. The situation is different when we consider the opticalspectral range. The quantitative spectroscopic analysis of this spectral range makes it possibleto determine the rotational velocities, effective temperatures, gravities and abundances ofthese stars (see e.g. the recent review by Martins, 2011, and references therein). Whenthe optical analyses are complemented with the information provided by other spectroscopicdiagnostics (mainly the UV) we can also constrain the wind properties of the analyzed stars.Nowadays we count with very powerful tools, such as advanced stellar atmosphere codesand stellar evolution models, which have allowed us to make a remarkable progress in ourknowledge of the physical and wind properties of massive stars (see review by Puls, 2008). Theoutcome of the quantitative spectroscopic analysis of medium and high resolution optical spec-tra of Galactic OB-type stars by means of modern stellar atmosphere codes is now acceptedto have reached a high degree of reliability (viz. Herrero et al., 2002; Repolust et al., 2004;Lefever et al., 2007; Markova & Puls, 2008; Sim´on-D´ıaz, 2010; Nieva & Przybilla, 2010). How-ever, it is important not to forget that our interpretation of these results may be clearly biasedin some cases, mainly due to observational limitations.The first point refers to the stellar luminosities, radii and masses. To obtain thesefundamental parameters we need to combine the derived spectroscopic parameters with in-formation about the distance and extinction to the star. At present, the distance to mostmassive stars in our Galaxy are poorly constrained and hence luminosities, radii and massesresulting from our analyses are somewhat uncertain in many cases. Table 1 illustrates howcritical is this point in the case of the O9 V star 10 Lac (d ∼
580 pc). Fortunately, this situationwill change very soon thanks to Gaia.The second point refers to binarity/multiplicity. Most or all massive stars are suspectedto be born as part of multiple systems (see e.g., Zinnecker & Yorke, 2007; Mason et al., 2009, . Sim´on-D´ıaz et al. R , L , and M due to errorpropagation of the uncertainties in stellar parameters (T eff and log g ) and distance are in-dicated separately. The later one (in brackets) clearly dominates. We need more accuratedistances. d =589 ±
79 pc (13%) Megier et al. (2009) T eff = 35000 ±
600 K m v =4.879 ± g = 3.87 ± B − V ) = -0.201 ± B − V ) = -0.27 Martins & Plez (2006) R / R ⊙ = 7.52 ± ± A v = 0.214 ± L / L ⊙ ) = 4.88 ± ± M v = -4.15 ± M / M ⊙ = 16 ± ± IACOBproject is following this approach in the case of Galactic stars. At present, we are performingthe analysis of the stars included in the
IACOB spectroscopic database following an auto-matic best-fit strategy based on a extensive grid of synthetic HHe spectra computed withthe FASTWIND stellar atmopshere code (see details in Sim´on-D´ıaz et al., 2011b). As a re-sults of this analysis, the project will provide a complete database of stellar parameters ofGalactic OB stars homogeneously determined. As commented above, the use of accuratedistances and multi-band photometry will be of crucial importance to complete the stellarparameters determined spectroscopically with luminosities, radii, and masses. In this sense,Gaia observations will come right on time.The final aim of the IACOB spectra and the associated database of stellar parameters(including also rotational velocities and abundances) is to increase the amount of observa-tional constraints which may help to advance in some of the still outstanding problems inthe field of massive stars. In addition, they can be used to study e.g. the kinematics of someof the Galactic OB clusters and associations, or the impact that massive stars have on theformation of other stellar objects (via their strong winds and ionizing fluxes). Finally, weplan to provide the spectral energy distributions (SEDs) predicted by the FASTWIND codefor all the analyzed stars so they can be then used in the study of the interstellar extinctionalong different line of sights (when combined with the observed SEDs provided by Gaia).
The IACOB project: synergies for the Gaia era
Acknowledgments