Free Access
Volume 530, June 2011
Article Number A11
Number of page(s) 15
Section Stellar atmospheres
Published online 27 April 2011

Online material

Appendix A: Comments on individual stars

Table A.1

Equivalent widths (in Å) and equivalent width ratios as measured for the O-type stars in our sample.

HD 64568 − This star was classified as O4 V((f)) (Garrison et al. 1977), O5 V (Loden 1965; Crampton 1972; Peton-Jonas 1981), and O3 V((f*)) (Walborn et al. 2002). The FUV/UV spectrum is also consistent with the O3 V((f*)) classification (Garcia & Bianchi 2004). The visual appearance of our spectrum is identical to that shown in Walborn et al., suggesting the same O3 V((f*)) designation. The discrepant spectral types assigned at different observational epochs might indicate that HD 64568 is a binary. This possibility seems to be supported by the detected Vr - variability (Solivella & Niemela 1986), but the good agreement between the model and the observed spectra (Paper II) argues in favour of the single-star hypothesis. The star has not been photometrically monitored and its short/long-term behaviour is completely unknown. Lacking direct evidence of possible binarity, we are inclined to consider HD 64568 as a single object with Vr - variations caused more likely by stellar pulsations (and/or wind variability). In this case then, the spectral type discrepancy could be due to reasons other than spectroscopic binarity.

HD 93204 is classified as O5 V((f)) by Walborn (1973) and considered as a standard of this subtype. Walborn et al. (2002) repeated this designation, whereas Mathys (1988) proposed O5.5 V((f)). Our high-resolution spectrum is identical to the one shown in Walborn et al. (2002). Consequently, we should denote the star O5 V((f)), but in our spectra, as well as in Walborn’s, He I+II λ4026   is of similar strength as He II λ4200 , which is the definition of an O6 subtype. The measured log W′ = −0.38 and log EW(4686) = −0.17 imply the O5.5 V classification. Within the limits of their V-band speckle interferometric observations, Mason et al. (2009) conclude that HD 93204 is a visually single object. To our knowledge, this star has never been monitored photometrically or spectroscopically. In Paper II, we have no problems obtaining good fits to all strategic helium and hydrogen lines using one set of parameters (including Vr and vsini ). Projected rotational velocities measured at different observational epochs agree perfectly (e.g., vsini  = 130, Conti & Ebbets 1977; vsini  = 130 km s-1, Penny 1996). All this suggests that HD 93204 is a spectroscopically single object.

We note that Walborn et al. (2010) have recently reclassified HD 93204 from O5((f)) to O5.5((fc)), where “fc” indicates the presence of C III λλ4647-4650-4652 emission lines of comparable strength to those of N III λλ4634-4640-4642 . Interestingly, in our high-resolution spectrum (R about ten times higher than that in the Walborn et al. observations), no sign of any C III emission can be seen, suggesting that the amount of C III emission is temporally variable in HD 93204. Similar results have been reported for three stars of the Of?n category: HD 108, HD 191612, and CPD −28 2561 (Walborn et al. 2010). The physical reason for the variable C III emission is still not well understood but given that HD 108 and HD 191612 have been recognized as long period binaries with magnetic fields, an interpretation in terms of orbital phase occultation of a localized C III emitting region has been suggested (Walborn et al. 2010 and references therein). If confirmed by means of a more detailed investigation, the single nature of HD 93204 would require an explanation of the variable C III emission that is different from that suggested by Walborn et al. (2010).

HD 93843  −  This star was initially classified as O6 III(f) (Walborn 1972), and later on reclassified as O5 III(f) (Walborn 1973). Applying the quantitative approach, Mathys (1988) assigned O5.5 III(f). The morphology of our spectrum agrees well with the O6 III(f) designation but with C III in emission. Following the definition of the new Ofc category (see above), we would denote it by O6 III(fc), that is one subtype later than the designation by Walborn et al. (2010), which is O5 III(fc). The measured log W′ = −0.37 is consistent with the O5.5 subtype. In the interferometric survey of Mason et al. (2009), HD 93843 is flagged as an object with a “null companion detection”. The star does not seem to show variations in its Vr   (Gies 1987). The model atmosphere analysis does not reveal any discrepancy in the shifts and widths of strategic lines (Paper II). Individual vsini  - estimates derived in different observational epochs agree within the corresponding uncertainties (e.g., vsini  = 120 km s-1, Conti & Ebbets 1977; vsini  = 95 km s-1, Howarth et al. 1997; vsini  = 100 km s-1, Penny 1996). We suggest that HD 93 843 is a spectroscopically single object.

CPD –59 2600  −  Walborn (1973) classified this star as O6 V((f)). The morphology of our spectrum resembles that of HD 101190, the primary standard for the O6 V((f)) subtype (Walborn & Fitzpatrick 1990), and consequently we assign O6 V((f)) to our target as well; log W′ = −0.17 and log EW(4686) = −0.24 indicate O6.5 V/III. A literature research shows that CPD –59 2600 has never been observed systematically. A comparison of individual vsini -estimates does not show any significant variations in this parameter (e.g., vsini  = 140 km s-1, Conti & Ebbets 1977; vsini  = 142 km s-1, Howarth et al. 1997; vsini  = 135 km s-1, Penny & Gies 2009). This finding together with the good agreement between synthetic and observed strategic lines (Paper II) suggests that CPD -59 2600 is likely a single object.

HD 63005 was classified as O7 by Loden (1965) and O6 V((f)) by Garrison et al. (1977). The general appearance of our spectrum agrees well with the O7.5 designation: He I λ4471   is slightly deeper than He II λ4541 , and there are both weak N III lines in absorption and missing C III λ4650 absorption. Since He II λ4686   is comparable in strength to He II λ4541 , the star might be a dwarf, but the strength of the N III λλ4634-4640-4642 emission lines are more consistent with a luminosity class “III” rather than “V” designation. Based on these considerations, we adopt O7.5 V((f)), but draw attention to its somewhat strong N III emission. The measured log W′ = −0.13 and log EW(4686) = −0.12 indicate O6.5 V. No reports about duplicity were found in the literature. The model atmosphere analysis has not revealed any spectral discrepancy (Paper II). Projected rotational velocities estimated at different epochs agree perfectly (e.g., vsini  = 73 km s-1, Penny 1996; vsini  = 74 km s-1, Howarth et al. 1997; vsini  = 80 km s-1, Penny 2004). With all this in mind, we consider HD 63005 a spectroscopically single object.

HD 152723, SB1  −  This star was classified as O7 by Schild et al. (1969) and O6.5 III(f) by Walborn (1972) and Garrison et al. (1977). The appearance of our spectrum is consistent with the O6.5 III(f) designation: He I+II λ4026   is slightly deeper than He II λ4200 ; He I λ4471   and He II λ4686 are weaker than He II λ4541 , and there is weak N III emission. The classification determined by means of the measured logW′ = −0.12 and log EW(4686) = −0.36 is also O6.5 III. Mason et al. (2009) resolved HD 152723 as a visual binary with an angular separation of 0.098”. Based on observed Vr  - variability, Fullerton et al. (1996) suggested that HD 152 723 is a SB1. This view was supported by Lefevre et al. (2009) who discovered photometric variations with a period of 0.395d. The discrepant strengths and widths of strategic helium and hydrogen lines (Paper II) also argue in favour of the binary hypothesis. Individual vsini - estimates available in the literature however do not deviate significantly, e.g., vsini  = 110 km s-1, Balona (1975); vsini  = 130 km s-1, Conti & Ebbets (1977); vsini  = 111 km s-1, Howarth et al. (1997); vsini  = 123 km s-1, Penny (1996). We consider HD 152723 as a single-lined SB.

HD 93160, SB1  −  Walborn (1972) denoted this star by O6 III(f). From the visual inspection of our spectrum, we classify it as O7 III(f): He I λ4471   of similar strength as He II λ4541 ; weak He II λ4686 absorption in combination with weak N III λλ4634-4640-4642 emission. The quantitative diagnostics, logW′ = −0.05 and log W′′ = 0.05, indicate a less luminous object, namely a dwarf, of the same O7 subtype. The spectral type discrepancy between the present morphological and Walborn’s classification might indicate that HD 93160 is a spectroscopic binary. This possibility was initially suggested by Gies (1987) based on Vr  - arguments, the latter however being questioned by Levato et al (1991). Our model atmosphere analysis has revealed a number of discrepancies in the optical spectrum, which might be interpreted as an indication of a close companion (Paper II). The binary hypothesis is supported by the large differences in vsini   derived in different observational epochs: e.g., vsini  = 180 km s-1, (Conti & Ebbets 1977); vsini  = 205 km s-1, (Uesugi & Fukuda 1995); vsini  = 145 km s-1 (Paper II). This star is very likely a SB1.

HD 94963 was previously classified as O6.5 III(f) by Walborn (1973) and O7 III by Garrison et al. (1977). Our spectrum of this star agrees with the O7.5 II subtype. Within the corresponding error, log W′ = −0.01 is consistent with the O7–7.5 subtype, while log W′′ = 0.32 corresponds to a supergiant or at least a giant. The discrepant classification attributed by various authors at different epochs might indicate that HD 94963 is a spectroscopic binary. This possibility seems to be supported by the large spread in individual vsini – estimates available in the literature (e.g., vsini  = 130 km s-1, Uesugi & Fukuda 1995; vsini  = 90 km s-1, Conti & Ebbets 1977). However, the star is regarded as photometrically stable (Kilkenny et al. 1998), with a constant Vr   (Gies 1987). In addition, the model atmosphere analysis does not reveal any discrepancy except for one: the He II λ4686   absorption line is peculiarly weak and narrow with a core that is red-shifted with respect to the position of the other spectral lines (Paper II). If not caused by wind asymmetries, the latter result might indicate a composite profile, consisting of an emission feature superimposed on the blue wing of an absorption profile. At least at present, we consider HD 94963 a single object with an asymmetric wind.

CPD –58 2620 was classified as O6.5 V((f)) by Walborn (1973) and O8 III by Morrell, Garcia, Levato (1988). The morphology of our spectrum is similar to that of λ Ori, the classification standard for O8 III((f)) (Walborn & Fitzpatrick 1990). However, in λ  Ori as well as in CPD –58 2620 the N III λλ4634-4640-4642 emission lines are very weak, and He II λ4686   is deeper than He II λ4541 , suggesting the “V((f))” rather than “III(f)” designation. Thus, we classify this star as O8 V((f)). From the measured equivalent widths, we estimate log W′ = −0.07 and log W′′ = 0.26, which is indicative of O7 III. CPD –58 2620 is a member of a visual binary with 3.7 arcsec separation. The star has been recognised “as a possible radial-velocity variable”, which however “does not show any obvious orbital trend in velocity from night to night” (Penny et al. 1993). No information about systematic photometric variations was found in the literature but a comparison of several UBV estimates listed in the Reed (2005) catalogue (V/125) suggests that this star might be photometrically variable. The excellent agreement between theoretical and observed strategic lines suggests that it is more likely to be a single object. Lacking any evidence of binarity, we consider CPD -58 2620 as a spectroscopically single object, but draw attention to the discrepancies in luminosity class between the various spectral diagnostics.

HD 69464, SB2?  −  Walborn (1972) classified this star as O6.5 Ib(f), and defined it as a classification standard for this spectral type/luminosity class (Walborn & Fitzpatrick 1990). Garrison et al. (1977) attributed O7 III(f). The visual appearance of our spectrum is similar to that of the spectrum shown in Walborn & Fitzpatrick (1990), with one important difference: in the latter, He II λ4686   is completely filled in by wind emission, while in our spectrum it appears as a weak absorption feature. Based on this notion and accounting for He I λ4471   being somewhat deeper than He II λ4541   in our spectrum as well as in that of Walborn & Fitzpatrick (1990), we re-classify the star from O6.5 Ib(f) to O7.5 II(f). Within the corresponding error, log W′ =−0.01 indicates the O7-7.5 subtype. In contrast, log W′′ = 0.28 is consistent with the star being a giant. Spectral anomalies such as those outlined above are usually interpreted as an indication of a companion. Unfortunately, HD 69464 has never been observed systematically, and no direct evidence in support or against this possibility exists. Individual vsini   determinations (e.g., vsini  = 71 km s-1, Howarth et al. 1997; vsini  = 82 km s-1, Penny 1996) and Vr - estimates (e.g., Vr  = 43 km s-1, Crampton 1972; Vr  = 45 km s-1, Paper II) seem to agree well, but this may still be due to observational selection. The correspondence between synthetic and observed lines is also good, except for He II λ4686 : the observed feature appears peculiarly narrow and weak and may show an inverse P Cygni profile (Paper II). If not due to wind variability or asymmetries, the latter finding would suggest that HD 69464 is a SB2. Systematic spectral/photometric observations are needed to check this possibility in the future.

HD 93222  −  Classified as O7 III((f)) by Walborn (1971, 1972), and again by Levato & Malaroda (1981) and Walborn & Fitzpatrick (1990). However, Massey et al. (2001) attributed O8 III((f)). The appearance of our spectrum differs significantly from that shown in Walborn & Fitzpatrick (1990), and resembles much more the spectral morphology of the O8 III((f)) standard λ Ori, which we adopt in our classification. The measured log W′ = −0.03 and log W′′ = 0.28 indicate a slightly earlier subtype, namely O7 III. HD 93222 is considered as non-variable in both photometry (e.g., Moffat 1977; Moffat & Seggeviss 1978) and Vr (e.g., Levato et al 1990). vsini - estimates from different observational epochs agree quite well (e.g., vsini  = 65, Conti & Ebbets 1977; vsini  = 77 km s-1, Howarth et al. 1997; vsini  = 77 km s-1, Penny 1996). The model atmosphere analysis does not uncover any spectral discrepancy (Paper II). All this suggests that HD 93222 is a spectroscopically single star.

HD 91824  −  Walborn (1972) denoted this star by O7 V((f)), confirmed by Garrison et al. (1977). From a visual inspection of our spectrum, we suggest O8 V((f)) since He II λ4686   and He I λ4471   are deeper than He II λ4541 ; numerous N III lines are in absorption, and weak C III in absorption and weak N III λλ4634-4640-4642 are in emission. The measured log W′ = −0.11 and log EW(4686) = −0.05 indicate O6.5 V. HD 91824 was found to be an irregular variable in both photometry (Lefevre et al. 2009) and Vr   (Feast 1958). Since the model atmosphere analysis (Paper II) as well as the classification analysis (present study) did not reveal any spectral discrepancy, we suggest that this variability is more likely due to stellar pulsation than to binarity. This possibility is further supported by the good agreement between individual vsini - estimates: vsini  = 67 km s-1 (Penny 1996) and vsini  = 65 km s-1 (Howarth et al. 1997).

CD -43 4690  −  Classified as O7.5 III(f) by Crampton (1971) and thereafter by Mathys (1988). The morphology of our spectrum agrees well with the O7 III(f) designation: He I λ4471   is as deep as He II λ4541 ; N III is in emission, and He II λ4686   is somewhat weaker than He II λ4541 . We measure log W′ = −0.20 and log EW(4686) = −0.23, which is indicative of the O6.5 V/III type. This star has never been observed systematically, neither photometrically nor spectroscopically. A comparison of individual data provided in the Reed (2005) catalogue did not reveal any significant variations in V and B − V on a longer (year) timescale. Based on several snapshots observations, Crampton (1972) conclude that this star is not a Vr - variable. The model atmosphere analysis does not reveal any spectral discrepancy (Paper II). We consider CD -43 4690 as a spectroscopically single object.

HD 92504 was denoted by O8.5 V (Walborn 1973), and this classification was repeated by Garrison et al. (1977). Turner (1977) assigned O9 V. The visual appearance of our spectrum is identical to that of the O8.5 V standard HD 46 149 (Walborn & Fitzpatrick 1990). We measure log W′ = 0.32 and log W′′ = 0.11, indicative of the O9 III/V type. Individual UBV measurements listed in the Reed (2005) catalogue suggest that the star is photometrically stable on a long (year) timescale. Individual Vr - estimates given in various catalogues (e.g., III/190 – Duflot et al. 1995; V/125 – Reed 2005) agree well. The model atmosphere analysis has not revealed any discrepancy in the spectrum (Paper II). This star is likely a single object.

HD 151003, SB1? was classified as O9 II (Walborn 1973), O9.5 III (Mathys 1988) and O9 Ib (Garrison et al. 1977). The morphology of our spectrum is in-between that of the classification standards HD 148 546 (O9 Ia) and ι Ori (O9 III) (Walborn & Fitzpatrick 1990), suggesting an intermediate O9 II classification. log W′ = 0.32 and log W′′ = 0.24 indicate O9 III. The differences in the spectral classifications of HD 151003 might indicate that it has a composite spectrum caused by binarity. Within the limits of the Mason et al. V-band interferometry, no indication of any companion was found. In the Turner et al. (2008) adaptive optics I-band photometric survey the star is flagged with “V”, i.e., ”one or more additional spectroscopic companions identified”. Based on Vr - arguments, Gies (1987) suspected that HD 151 003 is a SB1. This view is supported by discrepant widths of strategic helium and Balmer lines (Paper II). Thus, it seems likely that HD 151 003 is an SB1. Systematic photometric and/or radial velocity observations are needed to convincingly prove this possibility.

HD 152247, SB2  −  According to Walborn (1973), this star is a O9.5II/III and, similarly, a O9.5 III following Mathys (1988). Our spectrum is almost identical to that of HD 151003, suggesting the same O9 II classification. The measured log W′ = 0.39 is consistent with the O9 subtype; log W′′ = 0.19 corresponds to the luminosity class “III” rather than “II”. Balona (1983) reported that the visual brightness of HD 152247 is stable to within  ±0.05 mag. The star has never been monitored spectroscopically, but a comparison of individual estimates from the literature shows that its vsini   appears to be stable (e.g., vsini  = 110 km s-1Conti & Ebbets 1977; vsini  = 120 km s-1Penny 1996; vsini  = 112 km s-1Howarth et al. 1997), while its Vr   varies (Rabaud 1996; Sana et a. 2008). On the basis of the detection of an additional weak absorption component in He II λ4686 , Sana et a. (2008) suggested that HD 152247 is a SB2 consisting of an O9 III and an O9.7 V component. This result is additionally supported by detected discrepancies in the widths of helium and Balmer lines (Paper II). HD 152427 is definitely a SB2, where the secondary is significantly fainter (by 3 or more magnitudes to be consistent with the “null companion detection” of Mason et al. 2009) than the primary.

HD 302505  −  Classified as O9.5 III by Georgelin & Georgelin (1970) and O8.5 III by Garrison et al. (1977). Crampton (1972) listed it as B2 without, however, any reference to the original source. Our spectrum, visually, resembles that of ι Ori, the classification standard of the O9 III type (Walborn & Fitzpatrick 1990). log W′ = 0.16 and log W′′ = 0.22 indicate O8 III. The lack of consistency between the assigned spectral types might be interpreted as evidence of a companion. However, this view is not supported by the close agreement between the model and the observed spectra (Paper II). Individual UBV measurements listed in the Reed (2005) catalogue suggest that HD 302505 is photometrically stable on a longer timescale (within ΔV ≤  0.1 mag, Δ(B − V)    ≤  0.1 mag). Thus, we consider this star a single object, but future photometric and radial-velocity monitoring is required to check this view.

CPD –44 4865 has been classified as O9.5 Ib by Feast et al. (1961); Mathys (1988) reclassified it as O9.7 III. The general appearance of our spectrum resembles that of HD 48434, the classification standard for B0 III (Walborn & Fitzpatrick 1990). The only noticeable difference is that in CPD −44 4865, the lines He II λ4200   and He II λ4541   are definitely present, while they are missing in HD 48434. log W′ = 0.61 and log W′′ = 0.19 indicate O9.5 III, in good agreement with the classification by Mathys (1988). To our knowledge, CPD –44 4865 has never been systematically observed. In the Reed catalogue (2005), it is flagged as “RV var”, but no reference to the corresponding source(s) is provided. A comparison of individual Vr - estimates from different observational epochs does not show any significant variations (e.g., Vr  = 40 km s-1, the GCMRV; Vr  = 39.3 km s-1, the Reed 2005 catalogue). The model atmosphere analysis has not posed any problem: excellent fits were obtained for all strategic lines with one set of parameters (Paper II). All this suggests that CPD –44 4865 is likely a spectroscopically single object.

HD 69106  −  Morris (1961) classified this star as B0.5 III; Garrison et al. (1977) reclassified it as B0.5 IVnn. Our spectrum resembles that of τ Sco, the classification standard for B0.2 V (Walborn & Fitzpatrick 1990). The measured log W′ = 0.74 corresponds to O9.7. A literature research shows that HD 69106 has been recognised as a photometrically variable star, with a period of 1.48 d (Marchenko et al 1998). The star has not been monitored spectroscopically. Individual vsini - estimates agree well (e.g., vsini  = 329 km s-1, Howarth et al. 1997; vsini  = 316 km s-1, Balona 1975; vsini  = 328 km s-1, Conti & Ebbets 1977). Excellent fits have been derived for all strategic lines in the spectrum (Paper II). In the absence of direct evidence of binarity, we suggest that HD 69106 is more likely a single very late O-type dwarf undergoing stellar pulsations.

Appendix B: High-resolution atlas of our sample of stars

thumbnail Fig. B.1

High-resolution spectra of sample stars which have been classified originally as giants. Morphological classification as provided by Walborn (1972, 1973) using low resolution photographic spectra (with individual data from Garrison et al. 1977), together with our morphological classification based on high-resolution spectra. Confirmed/suspected SB1 and SB2 are also indicated.

Open with DEXTER

thumbnail Fig. B.2

As Fig. B.1, but for stars originally classified as dwarfs.

Open with DEXTER

© ESO, 2011

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