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58 Chapter 2. Multiwavelength approach to LS 5039 Apart from optical photometry in the Johnson filters, Strömgren and Hβ photometry have also been conducted. Kilkenny & Whittet (1993) reported the following Strömgren photometry for LS 5039: V = y = 11.223 ± 0.014, (b − y) = 0.766 ± 0.008, (v − b) = 0.624 ± 0.010, (u − b) = 1.204 ± 0.014, m1 = −0.142 ± 0.014 and c1 = −0.044 ± 0.022. They also computed the following de-redenned values: V = y = 11.223 ± 0.014, (b − y) = 0.743 ± 0.008, (v − b) = 0.597 ± 0.010, (u − b) = 1.202 ± 0.014, m1 = −0.146 ± 0.014 and c1 = −0.008 ± 0.022. Finally, Kilkenny (1993) reports the following Hβ photometry: β = 2.576 ± 0.010. 2.5.2 Spectral type Kilkenny (1993) was the first one to suggest a spectral type for LS 5039. He classified it as an O7IV star based on Strömgren and Hβ photometry. Later on, Motch et al. (1997) took a low resolution λλ 3800–4700 (all λ are expressed in ˚A) spectrum and a medium resolution red spectrum. Among O stars, those showing N iii in emission at λλ 4630–34 and He ii strongly in emission at λ 4686 are classified as Of stars. When the N iii is in emission and the He ii is weakly in absorption or emission they are classified as O(f). Finally, when the N iii is in emission and the He ii is strongly in absorption they are classified as O((f)). Motch et al. (1997) reported an O7V star with well marked He ii λ 4684 absorption and some evidence for weak N iii λλ 4634–4642 emission, and therefore suggested an O7V((f)) classification. No Hα emission was present in their medium resolution red spectrum. Clark et al. (2001) obtained higher resolution optical and near infrared spectroscopy of LS 5039. All Balmer lines were in absorption, preventing hence a classification as an Oe/Be star. The red-end spectrum (λλ 5650–7500) contained interstellar lines and helium lines in absorption. The blue-end spectrum (λλ 4050–4950) showed hydrogen Balmer series and He ii lines. The ratio between He ii λ 4541 and He i λ 4471 corresponded to a spectral type O6.5, while the presence of He ii 4686 strongly in absorption indicated that LS 5039 is still in the main sequence. Finally, the presence of very weak emission from N iii λλλ 4634–40–42 allowed them to add the ((f)) classification. Therefore, they classified LS 5039 as an O6.5V((f)) star. Furthermore, their K band (2.05–2.20 µm) and H band (1.49–1.72 µm) spectroscopy was perfectly consistent with such classification, and they stated that there was no evidence from any additional emission feature that could be attributed to emission from a jet or accretion disk.
2.5. The optical/IR star: LS 5039 59 2.5.3 Distance and its uncertainty Motch et al. (1997) proposed a distance of 3.1 kpc to LS 5039 based on the star color excess, and stated that this estimate could have a large uncertainty. This value was computed assuming an O7V((f)) spectral type. However, as we have just seen, recent observations by Clark et al. (2001) show that the optical companion has a spectral type of O6.5V((f)). On the other hand, old calibrations for the intrinsic color index and absolute magnitude (Johnson 1966, Deutschman et al. 1976) were used by Motch et al. (1997). Hence, we have performed a new estimate of the distance taking into account the new spectral type and more recent calibrations. The optical photometry available up to now and containing at least B and V magnitudes (see Table 2.5) comes from Drilling (1991), Lahulla & Hilton (1992) and Clark et al. (2001), and is listed in Table 2.6. Using an intrinsic color index of (B − V )0 = −0.30 ± 0.02 for an O6.5V star (Schaerer et al. 1996, Lejeune & Schaerer 2001), we can compute the color excess E(B − V ) for all the observations. Finally, using the relationship AV = [3.30 + 0.28 (B − V )0 + 0.04 EB−V ] E(B − V ) (Schmidt-Kaler 1982) and MV = −4.99 ± 0.3 for an O6.5V star (Vacca et al. 1996) we obtain the distance estimates listed in Table 2.6. The weighted mean of these values is 2.9 ± 0.3 kpc, and is the distance to LS 5039 used throughout this work. Finally, assuming that the Sun is at 8.5 kpc from the galactic center, we obtain a galactocentric distance of 5.8 ± 0.3 kpc for LS 5039. Table 2.6: Distance estimates to LS 5039 derived from optical photometry. V B − V E(B − V ) AV d [kpc] 11.23 ± 0.01 (a) 0.95 ± 0.01 (a) 1.25 ± 0.02 4.1 ± 0.1 2.68 ± 0.06 11.20 ± 0.02 (b) 0.95 ± 0.02 (b) 1.25 ± 0.03 4.1 ± 0.1 2.64 ± 0.06 11.33 ± 0.02 (c) 0.85 ± 0.02 (c) 1.15 ± 0.03 3.8 ± 0.1 3.26 ± 0.07 11.32 ± 0.01 (d) 0.85 ± 0.02 (d) 1.15 ± 0.03 3.8 ± 0.1 3.25 ± 0.07 (a) Drilling (1975, 1991). (b) Lahulla & Hilton (1992). (c) 1996 October observations by Clark et al. (2001). (d) 2000 September observations by Clark et al. (2001).
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UNIVERSITAT DE BARCELONA Departamen
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Per a la meva neboda Blanca, que va
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feina no presentada en aquesta tesi
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desfogar-nos conjuntament, per la s
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From the scientifical point of view
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Gràcies a la meva germana Nàdia,
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ii CONTENTS I Discovery and study o
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iv CONTENTS II A search for new mic
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viii Resum de la tesi d’Eddington
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xx Resum de la tesi valors força s
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xxxii BIBLIOGRAFIA
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2 Chapter 1. Introduction and backg
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Bibliography Ankay, A., Kaper, L.,
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BIBLIOGRAPHY 117 Schaerer, D., de K
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Part II A search for new microquasa
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122 Chapter 4. The cross-identifica
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