Äîêóìåíò âçÿò èç êýøà ïîèñêîâîé ìàøèíû. Àäðåñ îðèãèíàëüíîãî äîêóìåíòà : http://www.atnf.csiro.au/people/Angel.Lopez-Sanchez/proceedings/sergio2007.pdf Äàòà èçìåíåíèÿ: Mon Feb 4 02:38:22 2008 Äàòà èíäåêñèðîâàíèÿ: Mon Apr 14 04:19:42 2008 Êîäèðîâêà: Ïîèñêîâûå ñëîâà: trifid nebula

To appear in "Massive Stars: Fund. Param. and Circumst. Inter. (2007)"

RevMexAA(SC)

MASSIVE STARS AND THEIR SURROUNDING NEBULAE: A COMBINED APPROACH
S. Sim´n-D´az,1 G. Stasinska,1 J. Garc´a-Ro jas,2 C. Morisset,3 A. R. Lopez-S´nchez,2 and C. Esteban2 o i ´ i ´ a RESUMEN Presentamos los primeros resultados de un proyecto dedicado al estudio combinado de estrellas masivas y sus regiones H ii asociadas en la Galaxia. Mediante el estudio de regiones ionizadas por una unica estrella ´ pretendemos comprobar la validez de las predicciones de la nueva generacion de modelos de atm´sfera de ´ o estrellas masivas en t´rminos de distribucion de flujo ionizante. En nuestros an´lisis consideramos el efecto e ´ a de las posibles distribuciones de densidad del material ionizado. Para ello hacemos uso de varios tipos de observaciones, tanto estelares como de la regi´n H ii. o ABSTRACT We present the first results of a pro ject aimed at the combined study of massive stars and their surr nebulae by means of a detailed study of Galactic H ii regions ionized by only one massive star. With intend to check the validity of the new generation of massive star model atmosphere codes in terms of flux distribution. We take into account the effect of the nebular density distribution in our analyses. types of stellar and nebular observations have been collected for this purpose. ounding this, we ionizing Various

arXiv:astro-ph/0702363v1 14 Feb 2007

Key Words: STARS: EARLY-TYPE -- STARS: INDIVIDUAL: HD 37061 -- H II REGIONS -- ISM: IONIZATION MODELS -- ISM: INDIVIDUAL OBJECTS: M 43

1. INTRODUCTION The intense far ultraviolet radiation emitted by early OB-type stars ionizes the interstellar medium, generating the so-called H II regions. These ionized regions can be used to derive properties of the associated stellar population (e.g. star forming rates, age). However, since the properties of H II regions crucially depend on the spectral energy distribution (sed) of the massive star population, and this part of the stellar flux is generally unaccesible to direct observations, the predictions resulting from massive star atmosphere codes are a crucial ingredient. The new generation of nlte, line blanketed model atmosphere codes (Hubeny & Lanz, 1995, Hillier & Miller 1998, Pauldrach et al. 2001, Puls et al. 2005), which include a more realistic description of the physical processes characterizing the stellar atmosphere, produce quite different ionizing seds than the previous plane-parallel, nlte/lte, hydrostatic models (Mihalas & Auer 1970, Kurucz 1992, Kunze 1994). Some notes on this, and on the consequences on the ionization structure of H II regions, can be found in Gabler et al. (1989), Rubin et al. (1995), Na jarro et al. (1996), Sellmaier et al.
LUTh, Observatoire de Meudon, France. Instituto de Astrof´sica de Canarias, Spain. i 3 Instituto de Astronom´a, i Universidad Autonoma de M´xico, M´xico. ´ e e
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(1996) and Stasinska & Schaerer (1997). Although ´ new predictions seem to go in the right direction (viz. Giveon et al. 2002, Morisset et al. 2004), non-negligible differences can be found between the different stellar atmosphere codes (viz. Martins et al. 2005, Puls et al. 2005). We are performing a study of Galactic H ii regions ionized by only one massive star to check the validity of the ionizing seds predicted by the new generation of massive star model atmosphere codes. In forthcoming papers we will present the complete combined study of the various nebulae and their ionizing stars; here we show some preliminary results from our study of M 43.

2. OBSERVATIONAL DATASET Stellar and nebular observations were carried out with the Wide Field Camera (wfc; narrow-band imaging in H, H , [O III] and [S II]) and the Intermediate Resolution Spectrograph (ids; spectroscopy of the ionizing star in the range 4000 - 5000 ° + the A H region, and long slit nebular spectroscopy in the range 3600 - 9700 °); both instruments attached to A the Isaac Newton Telescope (int). The long slit nebular observations were divided into smaller apertures along the nebular radii. 1

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Fig. 2. Spatial variation of various nebular line ratios resulting from three cloudy constant density spherical models. Each model uses a different predicted sed. fastwind models are the ones used in Figure 1 (same color code); a tlusty model with the same stellar parameters as the fastwindmodel which best fits the optical HHe lines (Figure 1) has also been considered for comparison. Nebular observations from long slit spectra are also included.

Fig. 1. Fitting of fastwind synthetic profiles (broadened to v sin i = 210
km s-1 ) to the optical H and He lines of HD 37061. Two sets of stellar parameters are shown to illustrate the accuracy of the stellar parameters determination.

3. STELLAR AND NEBULAR ANALYSES M 43 is an apparently spherical H ii region, ionized by HD 37061 (classified as B1 V, though our spectrum clearly shows the He II 4541 line, indicating that the star is rather B0 V - B0.5 V). The stellar parameters of HD 37061 were obtained by visual fitting of fastwind (Puls et al. 2005) synthetic profiles to the optical H and He lines (see Figure 1). Once the sed resulting from the fastwind model was rescaled to fit Mv = 3.5 (from the stellar photometry and considering a distance of 450 pc), a value of log Q(H0 ) = 47.2 could be derived. This later value is in good agreement with the nebular H luminosity calculated from the wfc H image, indicating that the nebula is ionization bounded. From the nebular [S II] 6731/6716 line ratio we inferred Ne = 550 cm-3 . In a first approach, we have used the nebular abundances derived by Rodr´guez (1999) i 4. PHOTOIONIZATION MODELS Figure 2 illustrates three of the diagrams we use to compare the predictions of photoionization models (cloudy, Ferland et al. 1998) with the observed nebular constraints. The first one is an indicator of the nebular temperature, while the other two illustrate the nebular ionization structure. These plots compare three constant density spherical cloudy models: two of them take the seds from fastwind models with different stellar parameters, while the third one was calculated using the sed from a tlusty (Hubeny & Lanz, 1995) model with the same parameters as the fastwind model which best fits

the optical HHe lines. The differences between the photoionization models are important. Note, however, that geometries other than spherical and nonconstant density distributions can affect the result (Morisset et al. 2005). This will be also taken into account when inferring which model better fit the nebular constraints. In forthcoming papers we will present the complete analysis in detail. REFERENCES
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