Wind Momentum-luminosity Relationship Research Articles

The IACOB project

Context.The IACOB and OWN surveys are two ambitious, complementary observational projects which have made available a large multi-epoch spectroscopic database of optical high resolution spectra of Galactic massive O-type stars.Aims.Our aim is to study the full sample of (more than 350) O stars surveyed by the IACOB and OWN projects. As a first step towards this aim, we have performed the quantitative spectroscopic analysis of a subsample of 128 stars included in the modern grid of O-type standards for spectral classification. The sample comprises stars with spectral types in the range O3–O9.7 and covers all luminosity classes.Methods.We used the semi-automatizedIACOB-BROADandIACOB-GBAT/FASTWINDtools to determine the complete set of spectroscopic parameters that can be obtained from the optical spectrum of O-type stars. A quality flag was assigned to the outcome of theIACOB-GBAT/FASTWINDanalysis for each star, based on a visual evaluation of how the synthetic spectrum of the best fittingFASTWINDmodel reproduces the observed spectrum. We also benefitted from the multi-epoch character of the IACOB and OWN surveys to perform a spectroscopic variability study of the complete sample, providing two different flags for each star accounting for spectroscopic binarity as well as variability of the main wind diagnostic lines.Results.We obtain – for the first time in a homogeneous and complete manner – the full set of spectroscopic parameters of the “anchors” of the spectral classification system in the O star domain. We provide a general overview of the stellar and wind parameters of this reference sample, as well as updated recipes for the SpT–Teffand SpT–loggcalibrations for Galactic O-type stars. We also propose a distance-independent test for the wind-momentum luminosity relationship. We evaluate the reliability of our semi-automatized analysis strategy using a subsample of ~40 stars extensively studied in the literature, and find a fairly good agreement between our derived effective temperatures and gravities and those obtained by means of more traditional “by-eye” techniques and different stellar atmosphere codes. The overall agreement between the synthetic spectra associated with theIACOB-GBAT/FASTWINDbest fitting models and the observed spectra is good for most of the analyzed targets, but 46 stars out of the 128 present a particular behavior of the wind diagnostic lines that cannot be reproduced by our grid of spherically symmetric unclumped models. These are potential targets of interest for more detailed investigations of clumpy winds and/or the existence of additional circumstellar emitting components contaminating the wind diagnostic lines (e.g., disks, magnetospheres). Last, our spectroscopic variability study has led to the detection of clear or likely signatures of spectroscopic binarity in 27% of the stars and small amplitude radial velocity variations in the photospheric lines of another 30%. Additionally, 31% of the investigated stars show variability in the wind diagnostic lines.

Stellar and wind parameters of massive stars from spectral analysis

AbstractThe only way to deduce information from stars is to decode the radiation it emits in an appropriate way. Spectroscopy can solve this and derive many properties of stars. In this work we seek to derive simultaneously the stellar and wind characteristics of a wide range of massive stars. Our stellar properties encompass the effective temperature, the surface gravity, the stellar radius, the micro-turbulence velocity, the rotational velocity and the Si abundance. For wind properties we consider the mass-loss rate, the terminal velocity and the line–force parameters α, k and δ (from the line–driven wind theory). To model the data we use the radiative transport code Fastwind considering the newest hydrodynamical solutions derived with Hydwind code, which needs stellar and line–force parameters to obtain a wind solution. A grid of spectral models of massive stars is created and together with the observed spectra their physical properties are determined through spectral line fittings. These fittings provide an estimation about the line–force parameters, whose theoretical calculations are extremely complex. Furthermore, we expect to confirm that the hydrodynamical solutions obtained with a value of δ slightly larger than ~ 0.25, called δ-slow solutions, describe quite reliable the radiation line-driven winds of A and late B supergiant stars and at the same time explain disagreements between observational data and theoretical models for the Wind–Momentum Luminosity Relationship (WLR).

Effect of rotational mixing and metallicity on the hot star wind mass-loss rates

Hot star wind mass-loss rates depend on the abundance of individual elements. This dependence is usually accounted for assuming scaled solar chemical composition. However, this approach may not be justified in evolved rotating stars. The rotational mixing brings CNO-processed material to the stellar surface, increasing the abundance of nitrogen at the expense of carbon and oxygen, which potentially influences the mass-loss rates. We study the influence of the modified chemical composition resulting from the rotational mixing on the wind parameters, particularly the wind mass-loss rates. We use our NLTE wind code to predict the wind structure and compare the calculated wind mass-loss rate for the case of scaled solar chemical composition and the composition affected by the CNO cycle. We show that for a higher mass-fraction of heavier elements $Z/Z_\odot\gtrsim0.1$ the change of chemical composition from the scaled solar to the CNO-processed scaled solar composition does not significantly affect the wind mass-loss rates. The missing line force caused by carbon and oxygen is compensated for by nitrogen line force. However, for a very low-mass fraction of heavier elements $Z/Z_\odot\lesssim0.1$ the rotational mixing significantly affects the wind mass-loss rates. Moreover, the decrease of the mass-loss rate with metallicity is stronger at such low metallicities. We study the relevance of the wind momentum-luminosity relationship for different metallicities and show that for a metallicity $Z/Z_\odot\lesssim0.1$ the relationship displays a large scatter, which depreciates the use of this relationship at the lowest metallicities.

LIMB-DARKENED RADIATION-DRIVEN WINDS FROM MASSIVE STARS

We calculated the influence of the limb-darkened finite disk correction factor in the theory of radiation-driven winds from massive stars. We solved the 1-D m-CAK hydrodynamical equation of rotating radiation-driven winds for all three known solutions, i.e., fast, \Omega-slow and \delta-slow. We found that for the fast solution, the mass loss rate is increased by a factor \sim 10%, while the terminal velocity is reduced about 10%, when compared with the solution using a finite disk correction factor from a uniformly bright star. For the other two slow solutions the changes are almost negligible. Although, we found that the limb darkening has no effects on the wind momentum luminosity relationship, it would affect the calculation of synthetic line profiles and the derivation of accurate wind parameters.

A peculiar Of star in the Local Group galaxy IC 1613

Context. Results from the theory of radiatively driven winds are incorporated in stellar evolutionary and population synthesis models, and used in our interpretation of the observations of the deep Universe. Yet, the theory has been confirmed only until Small Magellanic Cloud metallicities. Analyses of O-stars at lower metallicities are needed to prove the theory. Aims. We have observed GHV-62024, an O6.5 IIIf star in the low-metallicity galaxy IC1613. According to a previous preliminary analysis this star could challenge the radiatively driven wind theory at low metallicities. Methods. Our observations were obtained with VIMOS at VLT, at R~2000 and were analysed using the latest version of the model atmosphere code FASTWIND, which includes N III Results. We obtain the stellar parameters and conclude that the star follows the average wind momentum-luminosity relationship (WLR) expected for its metallicity, but with a high value for the exponent of the wind velocity law, beta. We suggest that this high value may be reached because GHV-62024 could be a fast rotator seen at a low inclination angle. While the derived beta value does not change by adopting a lower wind terminal velocity, a wrong $V_\infty$ has a clear impact on the position of the star in the WLR diagram. The N and He abundances are very high, consistent with strong CNO mixing that could have been caused by the fast rotation, although we cannot discard a different origin. We find again the well-known mass-discrepancy. Conclusions. We conclude that the star follows the WLR expected for its metallicity. The results are consistent with GHV-62024 being a fast rotator seen close to pole-on, contaminated at the surface with CNO products and with a wind structure altered by the fast rotation without modifying the global WLR. We suggest that this could be a general property of fast rotators.

SLOW RADIATION-DRIVEN WIND SOLUTIONS OF A-TYPE SUPERGIANTS

The theory of radiation-driven winds succeeded in describing terminal velocities and mass loss rates of massive stars. However, for A-type supergiants the standard m-CAK solution predicts values of mass loss and terminal velocity higher than the observed values. Based on the existence of a slow wind solution in fast rotating massive stars, we explore numerically the parameter space of radiation-driven flows to search for new wind solutions in slowly rotating stars, that could explain the origin of these discrepancies. We solve the 1-D hydrodynamical equation of rotating radiation-driven winds at different stellar latitudes and explore the influence of ionization's changes throughout the wind in the velocity profile. We have found that for particular sets of stellar and line-force parameters, a new slow solution exists over the entire star when the rotational speed is slow or even zero. In the case of slow rotating A-type supergiant stars the presence of this novel slow solution at all latitudes leads to mass losses and wind terminal velocities which are in agreement with the observed values. The theoretical Wind Momentum-Luminosity Relationship derived with these slow solutions shows very good agreement with the empirical relationship. In addition, the ratio between the terminal and escape velocities, which provides a simple way to predict stellar wind energy and momentum input into the interstellar medium, is also properly traced.

Hot star wind models with new solar abundances

We compare the hot star wind models calculated assuming older solar abundance determination with models calculated using the recently published values derived from 3D hydrodynamical model atmospheres. We show that the use of new abundances with lower metallicity improves the agreement between wind observation and theory in several aspects: (1) The predicted wind mass-loss rates are lower by a factor of 0.76. This leads to a better agreement with mass-loss rate determinations derived from observations with account of clumping. (2) As a result of the lowering of mass-loss rates, there is a better agreement between predicted modified wind momentum-luminosity relationship and that derived from observations with account of clumping. (3) Both the lower mass fraction of heavier elements and lower mass-loss rates lead to a decrease of the opacity in the X-ray region. This has influence on the prediction of the X-ray line profile shapes. (4) There is a better agreement between predicted PV ionization fractions and those derived from observations.

Understanding B-type supergiants in the low metallicity environment of the SMC II

Despite a resurgence of effort over the last decade in the area of massive stars there is still ambiguity over their evolutionary path, contamination of their surface abundances and the behaviour of their stellar winds. Here 10 SMC B-type supergiants are analysed applying a unified model atmosphere code FASTWIND to intermediate resolution spectra from the ESO Multi Mode Instrument (EMMI) on the NTT telescope. Combined with the 8 targets analysed in paper 1, this work provides observational results on the properties of the winds and chemical compositions of B-type supergiants in the SMC. This paper emphasizes and substantiates the implications for stellar evolution from paper 1; that current theoretical models need to produce larger degrees of surface nitrogen enhancements at lower rotational velocities. In addition a significant discrepancy between theoretical and observed mass-loss rates is discussed which will have important implications for the rotational velocities obtained from stellar evolution calculations. Furthermore, an initial calibration of the wind-momentum luminosity relationship for B-type supergiants in a low metallicity environment (Z = 0.004) is presented.

NLTE models of line-driven stellar winds

New numerical models of line-driven stellar winds of late O stars are presented. Statistical equilibrium (NLTE) equations of the most abundant elements are solved. Properly obtained occupation numbers are used to calculate consistent radiative force and radiative heating terms. Wind density, velocity and temperature are calculated as a solution of model hydrodynamical equations. Contrary to other published models we account for a multicomponent wind nature and do not simplify the calculation of the radiative force (e.g. using force multipliers). We discuss the convergence behaviour of our models. The ability of our models to predict correct values of mass-loss rates and terminal velocities of selected late O stars (mainly giants and supergiants) is demonstrated. The systematic difference between predicted and observed terminal velocities reported in the literature has been removed. Moreover, we found good agreement between the theoretical wind momentum-luminosity relationship and the observed one for Cyg OB2 supergiants.

Understanding B-type supergiants in the low metallicity environment of the SMC

Spectroscopic analyses of 7 SMC B-type supergiants and 1 giant have been undertaken using high resolution optical data obtained on the VLT with UVES. FASTWIND, a non-LTE, spherical, line-blanketed model atmosphere code was used to derive atmospheric and wind parameters of these stars as well as their absolute abundances. Mass-loss rates, derived from H α profiles, are in poor agreement with metallicity dependent theoretical predictions. Indeed the wind-momenta of the SMC stars appear to be in good agreement with the wind-momentum luminosity relationship (WLR) of Galactic B-type stars, a puzzling result given that line-driven wind theory predicts a metallicity dependence. However the galactic stars were analysed using unblanketed model atmospheres which may mask any dependence on metallicity. A mean nitrogen enhancement of a factor of 14 is observed in the supergiants whilst only an enrichment of a factor of 4 is present in the giant, AV216. Similar excesses in nitrogen are observed in O-type dwarfs and supergiants in the same mass range, suggesting that the additional nitrogen is produced while the stars are still on the main-sequence. These nitrogen enrichments can be reproduced by current stellar evolution models, which include rotationally induced mixing, only if large initial rotational velocities of 300 km s -1 are invoked. Such large rotational velocities appear to be inconsistent with observed ν sin i distributions for O-type stars and B-type supergiants, Hence it is suggested that the currently available stellar evolution models require more efficient mixing for lower rotational velocities.

Bright OB stars in the Galaxy

We study mass-loss and wind momentum rates of 29 Galactic O-type stars with luminosity classes I, III and V by means of a pure Hα profile analysis and investigate to what extent the results compare to those originating from a state-of- the-art, complete spectral analysis. Our investigation relies on the approximate method developed by Puls et al. (1996) which we have modified to account for the effects of line-blanketing. Effective temperatures and gravities needed to obtain quanti- tative results from such a simplified approach have been derived by means of calibrations based on most recent spectroscopic NLTE analyses and models of Galactic stars by Repolust et al. (2003) and Martins et al. (2002). Comparing (i) the derived wind- densities to those determined by Repolust et al. (2003) for eleven stars in common and (ii) the Wind-momentum Luminosity Relationship (WLR) for our sample stars to those derived by other investigations, we conclude that our approximate approach is actually able to provide consistent results. Additionally, we studied the consequences of fine tuning some of the direct and indirect parameters entering the WLR, especially by accounting for different possible values of stellar reddening and distances. Combining our data set with the corresponding data provided by Herrero et al. (2002) and Repolust et al. (2003) we finally study the WLR for the largest sample of Galactic O-type stars gathered so far, including an elaborate error treatment. The established disagreement between the theoretical predictions and the observed WLRs being a function of luminosity class is suggested to be a result of wind clumping. Different strategies to check this hypothesis are discussed, particularly by comparing the Hα mass-loss rates with the ones derived from radio observations.

The Wind Momentum-Luminosity relationship: blue supergiants in the spiral galaxy NGC 300

We have carried out the wind analysis of six A-type supergiants in NGC 300. The derived Wind Momentum-Luminosity Relationship is compared with that of Galactic and M 31 blue supergiants and with theoretical models.

Parameters of massive OB stars

I review our knowledge about effective temperatures and masses of massive OB stars paying special attention to results recently obtained using new atmospheric models including sphericity, mass-loss and line-blanketing. The new temperature scales for O dwarfs and supergiants are lower than previously accepted. No systematic mass discrepancy is found among O supergiants, although individual problematic cases still remain. It is shown that model atmospheres give answers consistent with binary systems. Good agreement is found between theoretical predictions and observations of the Wind Momentum-Luminosity relationship for Galactic O-type supergiants. Finally, I review the status of the WLR in M33.

Space Telescope Imaging Spectrograph Ultraviolet Spectroscopy of Early B Supergiants in M31

We analyze Space Telescope Imaging Spectrograph (STIS) spectra in the 1150-1700 A wavelength range obtained for six early B supergiants in the neighboring galaxy M31. Because of their likely high (nearly solar) abundance, these stars were originally chosen to be directly comparable to their Galactic counterparts and represent a much needed addition to our current sample of B-type supergiants, in our efforts to study the dependence of the wind momentum-luminosity relationship on spectral type and metallicity. As a first step to determine wind momenta we fit the P Cygni profiles of the resonance lines of N V, Si IV, and C IV with standard methods and derive terminal velocities for all of the STIS targets. From these lines we also derive ionic stellar wind column densities. Our results are compared with those obtained previously in Galactic supergiants and confirm earlier claims of normal wind line intensities and terminal velocities in M31. For one-half of the sample we find evidence for an enhanced maximum turbulent velocity when compared to Galactic counterparts.

Revised Stellar Temperatures for Magellanic Cloud O Supergiants fromFar Ultraviolet Spectroscopic Explorerand Very Large Telescope UV‐Visual Echelle Spectrograph Spectroscopy

We have undertaken quantitative analysis of four LMC and SMC O4-9.7 extreme supergiants using far- ultraviolet FUSE, ultraviolet IUE/Hubble Space Telescope, and optical Very Large Telescope UV-Visual Echelle Spectrograph spectroscopy. Extended, non-LTE model atmospheres that allow for the consistent treatment of line blanketing, developed by Hillier & Miller, are used to analyze wind and photospherics spec- tral features simultaneously. Using Hto constrain mass-loss rates, He i-He ii photospheric lines reveal stel- lar temperatures that are systematically (5-7.5 kK) and substantially (15%-20%) lower than previously derived from unblanketed, plane-parallel, non-LTE photospheric studies. We have confidence in these revisions since derived temperatures generally yield consistent fits across the entire 912-7000 Aobserved spectral range. In particular, we are able to resolve the UV-optical temperature discrepancy identified for AzV 232 (O7 Iaf + ) in the SMC by Fullerton and coworkers. The temperature and abundance sensitivity of far-ultraviolet, UV, and optical lines are discussed. '' Of '' classification criteria are directly linked to (strong) nitrogen enrichment (via N iii � 4097) and (weak) carbon depletion (via C iii �� 4647-4651), providing evidence for mixing of unprocessed and CNO-processed material at their stellar surfaces. Oxygen abundances are more difficult to constrain, except via O ii lines in the O9.7 supergiant, for which it is also found to be somewhat depleted. Unfortunately, He/H is very difficult to determine in individual O super- giants because of uncertainties in microturbulence and the atmospheric scale height. The effect of wind clumping is also investigated, for which P v �� 1118-1128 potentially provides a useful diagnostic in O star winds, unless phosphorus can be independently demonstrated to be underabundant relative to other heavy elements. Revised stellar properties affect existing calibrations of (1) Lyman continuum photons—a factor of 2 lower for the O4 supergiant—and (2) kinetic energy released into the ISM by O supergiants. Our results also have importance for the calibration of the wind momentum-luminosity relationship for OB stars, particularly since the stars studied here are among the visually brightest OB stars in external galaxies. Subject headings: stars: early-type — stars: fundamental parameters — stars: mass loss — ultraviolet: stars

The evolutionary status of Sher 25 – implications for blue supergiants and the progenitor of SN 1987A

The blue supergiant Sher 25 in the massive Galactic cluster NGC 3603 is surrounded by a striking emission line nebula. The nebula contains an equatorial ring and probable bi-polar outflows, and is similar in morphology, mass and kine- matics to the shell now visible around SN 1987A. It has been suggested that both nebulae were ejected while Sher 25 and the progenitor of SN 1987A were in previous red supergiant phases. In the case of Sher 25 this is based on the qualitative strengths of nebular (Nii) emission which is indicative of nitrogen enriched gas. This gas may have been dredged up to the stellar surface by convective mixing during a previous red supergiant phase. We present optical high-resolution spectra of Sher 25 and a model photosphere and unified stellar wind analysis which determines the atmospheric parameters, mass-loss rate and photospheric abundances for C, N, O, Mg, and Si. We compare these results, in particular CNO, to other Galactic B-type supergiants and find that Sher 25 does not appear extreme or abnormal in terms of its photospheric nitrogen abundance. The C/ Na nd N/O ratios are compared to surface abundances predicted by stellar evolutionary calculations which assume the star has gone through a red supergiant phase and convective dredge-up. In particular we find that the N/O abundance is incompatible with the star having a previous red supergiant phase, and that the nebulae is likely to have been ejected while the star was a blue supergiant. The results are compatible with some degree of rotationally induced mixing having occurred while the star was on or near the main-sequence. This is similar to what has recently been found for nebulae surrounding LBVs. In addition our wind analysis suggests the star currently has a relatively normal mass-loss rate in comparison with other Galactic B-type supergiants and sits comfortably within the wind momentum-luminosity relationship. In light of the evidence regarding massive evolved early-type stars in the Galaxy we suggest there is no object which shows any evidence of having had a previous red supergiant phase and hence of undergoing blue loops in the HR diagram.

An analysis of STIS HST UV spectra of M 33 early B supergiants

We present terminal velocities of M 33 B-supergiants, obtained from STIS HST spectra as part of our programme to investigate the Wind Momentum { Luminosity Relationship (WLR) in the Local Group. Terminal velocities are derived from their N v ,C iv, and Si iv resonance lines in UV spectra. Comparing with IUE spectra of Galactic B-supergiants we found evidence of low metallicity in three of our objects. The terminal velocities are consistent with the corresponding values of Galactic stars, except for B-133. For this star we nd a very large v1 and ar ed Siiv component deeper than the blue one, that might be an indication of binarity. The average ratio between terminal and turbulent wind velocities is 0.25, well above the value found for Galactic stars.

The Spectral Energy Distribution and Mass‐Loss Rate of the A‐Type Supergiant Deneb

A stellar wind module has been developed for the PHOENIX stellar atmosphere code for the purpose of computing non-LTE, line-blanketed, expanding atmospheric structures and detailed synthetic spectra of hot luminous stars with winds. We apply the code to observations of Deneb, for which we report the first positive detections of millimeter and centimeter emission (obtained using the Submillimeter Common-User Bolometric Array and the Very Large Array) as well a strong upper limit on the 870 ?m flux (using the Heinrich Hertz Telescope). The slope of the radio spectrum shows that the stellar wind is partially ionized. We report a uniform-disk angular diameter measurement = 2.40 ? 0.06 mas from the Navy Prototype Optical Interferometer (NPOI). The measured bolometric flux and corrected NPOI angular diameter yield an effective temperature of 8600 ? 500 K. Least-squares comparisons of synthetic spectral energy distributions from 1220 ? to 3.6 cm with the observations provide estimates for the effective temperature and the mass-loss rate of 8400 ? 100 K and (8 ? 3) ? 10-7 M? yr-1, respectively. This range of mass-loss rates is consistent with that derived from high-dispersion UV spectra when non-LTE metal-line blanketing is considered. We are unable achieve a reasonable fit to a typical H? P Cygni profile with any model parameters over a reasonable range. This is troubling because the H? profile is the observational basis for the wind momentum-luminosity relationship.

Spectroscopy of Blue Supergiants in the Spiral Galaxy NGC 300

We have obtained VLT low-resolution (~5 ?) multiobject spectroscopy in the 4000-5000 ? spectral range of about 70 blue supergiant candidates in the Sculptor Group spiral galaxy NGC 300, selected from previous wide-field photometry. Of the 62 spectroscopically confirmed blue supergiants, with spectral types ranging from late O to F, 57 have types between early B and mid-A. We present a detailed spectral catalog containing identification, magnitudes, colors, and spectral types. We employ synthetic spectra calculated from blue supergiant model atmospheres for different metallicities to determine metal abundances for two A0 supergiants of the sample. In agreement with the expectations, the star closer to the galactic center is found to be more metal-rich than the object at a larger galactocentric distance. We will employ this technique on the whole supergiant sample to determine the stellar abundance gradient in the disk of NGC 300, together with the internal reddening from a comparison of the observed versus synthetic colors. This will allow, among other things, an accurate calibration of the effect of metallicity on the Cepheid period-luminosity relation. Using the Balmer H? line profile, we have estimated the mass-loss rate for one of the brightest A2 supergiants in the sample. Under additional reasonable assumptions, we determined the wind momentum of the star and compared it with the value expected from the empirical wind momentum-luminosity relationship (WLR) for A-type supergiants of Kudritzki et al. Good agreement is obtained. We will derive mass-loss rates and wind momenta for all stars in our sample from the H? line profiles in forthcoming work, and we will then thoroughly test the usefulness of the WLR for distance measurement out to about 15 Mpc.

Chemical abundances and winds of massive stars in M31: a B-type supergiant and a WC star in OB 10

We present high quality spectroscopic data for two massive stars in the OB 10 association of M31, OB 10-64 (B0 Ia) and OB 10-WR1 (WC6). Medium resolution spectra of both stars were obtained using the ISIS spectrograph on the William Herschel Telescope. This is supplemented with Hubble Space Telescope STIS UV spectroscopy and Keck I HIRES data for OB 10-64. A non-local thermodynamic equilibrium (LTE) model atmosphere and abundance analysis for OB 10-64 is presented, indicating that this star has similar photospheric CNO, Mg and Si abundances to solar neighbourhood massive stars. A wind analysis of this early B-type supergiant reveals a mass-loss rate of M˙=1.6×10−6 M⊙ yr−1, and v∞=1650 km s−1. The corresponding wind momentum is in good agreement with the wind momentum–luminosity relationship found for Galactic early-B supergiants. Observations of OB 10-WR1 are analysed using a non-LTE, line-blanketed code, to reveal approximate stellar parameters of log L/L⊙∼5.7, T∗∼75 kK, v∞∼3000 km s−1, M˙/(M⊙ yr−1)∼10−4.3 adopting a clumped wind with a filling factor of 10 per cent. Quantitative comparisons are made with the Galactic WC6 star HD 92809 (WR23) revealing that OB 10-WR1 is 0.4 dex more luminous, though it has a much lower C/He ratio (∼0.1 versus 0.3 for HD 92809). Our study represents the first detailed, chemical model atmosphere analysis for either a B-type supergiant or a Wolf–Rayet (WR) star in Andromeda, and shows the potential of how such studies can provide new information on the chemical evolution of galaxies and the evolution of massive stars in the local Universe.