Mapping the core of the Tarantula Nebula with VLT-MUSE II. The spectroscopic Hertzsprung-Russell diagram of OB stars in NGC 2070
N. Castro, P. A. Crowther, C. J. Evans, J. S. Vink, J. Puls, A. Herrero, M. Garcia, F. J. Selman, M. M. Roth, S. Simón-Díaz
AAstronomy & Astrophysics manuscript no. AA_2020_4_ncastro_astroph © ESO 2021February 9, 2021
Mapping the core of the Tarantula Nebula with VLT-MUSE (cid:63)
II. The spectroscopic Hertzsprung-Russell diagram of OB stars in NGC 2070
N. Castro , P. A. Crowther , C. J. Evans , J. S. Vink , J. Puls , A. Herrero , , M. Garcia , F. J. Selman , M. M. Roth and S. Simón-Díaz , Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germanye-mail: [email protected] Department of Physics & Astronomy, University of She ffi eld, Hounsfield Road, She ffi eld, S3 7RH, UK UK Astronomy Technology Centre, Royal Observatory, Blackford Hill, Edinburgh, EH9 3HJ, UK Armagh Observatory and Planetarium, College Hill, Armagh BT61 9DG, Northern Ireland, UK LMU München, Universitätssternwarte Scheinerstr. 1, D-81679 München, Germany Instituto de Astrofísica de Canarias, La Laguna, Tenerife, Spain Departamento de Astrofísica, Universidad de La Laguna, Tenerife, Spain Centro de Astrobiología CSIC-INTA. Crtra. de Torrejón a Ajalvir km 4. E-28850 Torrejón de Ardoz, Madrid, Spain European Southern Observatory, Alonso de Cordova 3107 Vitacura Casilla, 7630355, Santiago, ChileFebruary 9, 2021
ABSTRACT
We present the spectroscopic analysis of 333 OB-type stars extracted from VLT-MUSE observations of the central 30 ×
30 pc ofNGC 2070 in the Tarantula Nebula on the Large Magellanic Cloud, the majority of which are analysed for the the first time. Thedistribution of stars in the spectroscopic Hertzsprung-Russell diagram (sHRD) shows 281 stars in the main sequence. We find twogroups in the main sequence, with estimated ages of 2.1 ± ± / or significant nebular contamination a ff ecting the analysis.As in previous studies, stellar masses derived from the sHRD are systematically larger than those obtained from the conventionalHRD, with the di ff erences being largest for the most massive stars. Additionally, we do not find any trend between the estimatedprojected rotational velocity and evolution in the sHRD. The projected rotational velocity distribution presents a tail of fast rotatorsthat resembles findings in the wider population of 30 Doradus. We use published spectral types to calibrate the He i λ / He ii λ ff ective temperature. Key words.
Stars: early-types – Stars: fundamental parameters – open clusters and associations: individual: NGC2070 – Galaxies:individual: Large Magellanic Cloud
1. Introduction
Massive stars are thought to drive the chemical and dynami-cal evolution of galaxies (Ceverino & Klypin 2009; Kennicutt& Evans 2012). They are also thought to be strong candidatesfor the re-ionisation of the early Universe (e.g. Robertson et al.2010). However, the formation and evolution of stars more mas-sive than 10 M (cid:12) still hold many unanswered questions (Langer2012). These uncertainties quickly grow as we move up to highermasses in the Hertzsprung-Russell diagram (HRD), particularlyfor the most massive stars (with M > M (cid:12) ) and beyond thehydrogen core-burning phase (Vink et al. 2015).The HRD is a powerful tool for investigating the evolutionof massive stars, particularly the influence that factors such asmass, rotation, metallicity, magnetic fields, and binarity have ontheir main sequence lifetimes, later evolutionary phases, and ul-timate fates (e.g. Shu & Lubow 1981; Maeder 1987; Maeder &Meynet 2000; de Mink et al. 2014). Disentangling the respectiveroles of these factors to chart the various evolutionary paths re- (cid:63) Based on observations made with ESO telescopes at the Paranalobservatory under programme ID 60.A-9351(A). quires homogeneous, statistically robust studies of the physicalproperties of populations of massive stars.Historically, photometric studies were the sole route for in-vestigating large stellar samples (e.g. Fitzpatrick & Garmany1990; Massey 2002), but the degeneracy of the optical colours toderive the e ff ective temperatures (T e ff ) of OB-type stars (Hum-mer et al. 1988) from such an approach limits any insight intostellar evolution (Larsen et al. 2011). More recently, spectro-scopic surveys have transformed the field, enabling observationsof large samples for a detailed quantitative study in the MilkyWay (e.g. Simón-Díaz et al. 2017; Martins et al. 2017), the Mag-ellanic Clouds (e.g. Evans et al. 2004, 2011; Massey et al. 2004;Ramachandran et al. 2018, 2019; Dufton et al. 2019), and innearby star-forming galaxies in the Local Group (e.g. Urbanejaet al. 2003; Castro et al. 2012).Based on this wealth of spectroscopic data, the spectroscopicHRD (sHRD; L ≡ T ff / g ; Langer & Kudritzki 2014) can pro-vide insights into stellar evolution (see also Castro et al. 2014).The sHRD, which is the inverse of the flux-weighted gravity in-troduced by Kudritzki et al. (2003), does not require knowledgeof the extinction or distance to the targets and can be calculatedfrom the stellar analyses. In contrast to the classical Kiel diagram Article number, page 1 of 19 a r X i v : . [ a s t r o - ph . S R ] F e b & A proofs: manuscript no. AA_2020_4_ncastro_astroph (T e ff – log g ), the sHRD sorts stars according to their proximityto the Eddington limit. Castro et al. (2014, 2018b) proposed em-pirical anchors for the stellar evolution of massive stars in theMilky Way and the Small Magellanic Cloud (SMC) based onthe sHRD, such as the position of the zero age main sequence(ZAMS) and the terminal age main sequence (TAMS). Theseprovide robust targets for theories of massive-star evolution, in-cluding constraints on parameters such as rotation, convectiveovershooting, and metallicity (Brott et al. 2011; Ekström et al.2012; Sanyal et al. 2017; Higgins & Vink 2019). In this study, weextend this approach to the massive-star population of the LargeMagellanic Cloud (LMC), which has an intermediate metallicity( Z / Z (cid:12) = .
5) between that of the Milky Way and the SMC.Although conceptually designed as a cosmology machine,the Multi-Unit Spectroscopic Explorer (MUSE; Bacon et al.2014) on the Very Large Telescope (VLT) presents exciting ca-pabilities for the spectroscopy of stellar populations (see the re-view by Roth et al. 2019) and a leap forward from pioneeringstudies based on 3D spectroscopy (e.g. Kamann et al. 2013).This unique integral field spectrograph with a large field-of-view (1 (cid:48) × (cid:48) ), excellent image quality, and high e ffi ciency en-ables a novel approach to studying populations of massive stars,somewhere in between traditional photometric and multi-objectspectroscopic surveys. MUSE also overcomes selection biasescaused by extinction. Internal extinction may be significantwithin star-forming galaxies, and O stars may be missed in sur-veys where targets were selected based on optical colours only(e.g. Garcia et al. 2019). MUSE capabilities in the analysis ofyoung stellar populations have been explored in recent years innearby clusters (e.g. Weilbacher et al. 2015; Zeidler et al. 2018),the Magellanic Clouds (e.g. McLeod et al. 2019; Bodensteineret al. 2020), and, even farther away in galaxies outside the LocalGroup (e.g. NGC300 and Leo P; Roth et al. 2018; Evans et al.2019).The Tarantula Nebula in the LMC is the most luminous star-forming complex in the Local Group (Kennicutt 1984; Crowther2019). The inner part of the Tarantula, NGC 2070, hosts a well-known rich population of OB-type and Wolf-Rayet (W-R) stars(e.g. Melnick 1985; Selman et al. 1999; Evans et al. 2011).Moreover, in the core of NGC 2070 lies the young massivecluster R136, home to the most massive stars known to date(Crowther et al. 2010; Bestenlehner et al. 2020).To test the unique capabilities of MUSE, NGC 2070 was ob-served as part of its Science Verification (SV) programme. TheSV observations have provided the most complete spectroscopiccensus of the region to date (Castro et al. 2018a, hereafter PaperI). Here we apply a similar approach to that of Castro et al. (2014,2018b) to the MUSE data to investigate massive-star evolutionat the metallicity of the LMC (and notably in a young regionthat is still undergoing active star formation). A big advantageof NGC 2070 compared to the samples in the Milky Way and theSMC (Castro et al. 2014, 2018b) is that it is a more homogeneouspopulation in terms of age, facilitating the study of the proper-ties of the most massive stars. Large and homogeneous studiesare crucial to reducing the biases outlined by Castro et al. (2014)and providing reliable empirical boundaries for theoretical mod-els of stellar evolution.This article is structured as follows. Section 2 briefly intro-duces the data and the sample for quantitative analysis. Sec-tion 3 describes the methods used to estimate physical param-eters and to classify the spectra. Section 4 introduces the sHRDfor NGC 2070, and Sect. 5 discusses the ages, masses, and rota-tion rates of the sample. We summarise our findings in Sect. 6. Fig. 1.
Spatial distribution of the sample stars (open red circles) overlaidon the continuum-integrated 2 (cid:48) × (cid:48) MUSE mosaic in NGC 2070 (seePaper I). The core of the cluster, R136, is marked.
2. Data and sample selection
The central 2 (cid:48) × (cid:48) of NGC 2070 was observed with a mosaicof four MUSE pointings as part of the SV programme in Au-gust 2014. The data were obtained with the natural seeing mode(with spatial sampling of 0 (cid:48)(cid:48) . R ∼ α .The observations, data reduction, and a comprehensive cata-logue of early-type stars in the MUSE mosaic were presentedin Paper I. For the quantitative analysis presented here, weused spectra extracted from the 4 ×
600 s exposures and limitedour census to OB-type spectra with signal-to-noise ratios (S / N)greater than 50. This enabled a robust study of their physicalproperties from comparison with synthetic spectra from modelatmospheres.We excluded stars with T e ff <
10 000 K as well as W-R stars(and related stars) with He ii λ / N >
50. Their spatial dis-tribution in the MUSE mosaic is shown in Fig. 1, and their posi-tions are listed in Table 2.Each spectrum was visually examined to discard compositespectra due to project or unresolved stars or binaries. Neverthe-less, unresolved components contributing to the spectra must bekept in mind in the conclusions. The R136 cluster at the coreof NGC 2070 is unresolved and is not included in this study(Fig. 1). A parallel project using the narrow-field mode (Lei-bundgut et al. 2019) of MUSE to study R136 with superior spa-tial resolution is ongoing.
3. Spectral analysis
The MUSE wavelength range does not include the traditional di-agnostic features (e.g. He i λ ii λ iii λ i ( λλ ii ( λλ α and H β are included in the MUSE spectra, but in a region as Article number, page 2 of 19. Castro et al.: The sHRD of OB stars in NGC 2070
Fig. 2.
Estimated e ff ective temperatures (T e ff , top panel), gravities(log g , middle panel), and luminosities (log L / L (cid:12) , bottom panel) fromthe MUSE data compared with results from the VFTS for the 42 starsin common. (Sabín-Sanjulián et al. 2014, 2017; McEvoy et al. 2015;Ramírez-Agudelo et al. 2017; Garland et al. 2017; Schneider et al.2018b). young as NGC 2070, these are generally contaminated by strongnebular emission from the surrounding excited gas.Our sample was analysed using a grid of hydrogen and he-lium (HHe) fastwind models (Santolaya-Rey et al. 1997; Pulset al. 2005; Rivero González et al. 2012). fastwind calculatesthe atmosphere and line formation in spherical symmetry, withan explicit treatment of the stellar wind and taking into accountnon-local thermodynamic equilibrium. The analysis used a gridsimilar to the one described by Castro et al. (2018b) but nowcalculated with the LMC metallicity (i.e. Z / Z (cid:12) = . < T e ff <
67 000 K (insteps of 1000 K) and 0.8 < log g < Q = −
14 (Puls et al. 1996, 2000). In the upper part of the HRD,stronger stellar winds are expected to a ff ect lines such asHeII λ He ) were set to 0 .
09. Castro et al. (2018b)tested di ff erent surface helium abundances and concluded that itwas not possible to constrain the He abundance with the modestspectral resolution.The analysis used a similar χ algorithm to the one used byCastro et al. (2012, 2018b). The algorithm simultaneously fitsthe available He lines and, where possible, the wings of the H β profile for each star and searches for the set of parameters thatbest reproduces the observations (see also Urbaneja et al. 2005;Evans et al. 2007). H β is included to try to constrain the surfacegravity, but we note that it is influenced in many instances bythe strong nebular contribution and / or strong stellar wings forthe most massive stars (Castro et al. 2018b). Comparisons withprevious studies in the LMC (see Sect. 3.1) reinforce the factthat the reader should be cautious of the quoted gravities, butthey serve as a first estimate to investigate the overall sHRD ofthe region.Projected rotational velocities ( v sin i ) were estimated by fit-ting the He lines with the fastwind model from the first iterationof the fitting algorithm, where the model is broadened assum-ing only contributions from stellar rotation and the instrumentalresolution. The atmospheric analysis was then repeated with thenew v sin i estimate until convergence. Macroturbulence is ex-pected to be an important additional broadening factor in somestars in the upper part of the sHRD (see Grassitelli et al. 2016;Simón-Díaz et al. 2017). However, given the limitations of themodest spectral resolution, we do not include this in our analy-sis, with the result that some of the quoted v sin i values may beoverestimated.The ionisation balance of He ii / He i is used to estimate T e ff for spectra where both species are available. However, in theearliest O-type stars, we lack suitable He i lines, and He ii is ab-sent for all but the earliest B-types. For these parts of the sam-ple, our analysis rests on the accuracy of the HHe models, andsome degeneracy is to be expected (and is indirectly includedin the estimated errors from the algorithm; see Sect. 3 of Cas-tro et al. 2018b). Nebular contamination in the helium lines maybe expected after the sky subtraction, also a ff ecting the e ff ectivetemperatures derived in our analysis. The accuracy of the tem-peratures from our pure HHe analysis is discussed in the nextsections (see also the discussion in Castro et al. 2018b). The pa-rameters derived from this work are summarised in Table 2. We cross-matched our sample with stars observed as part of theVLT-FLAMES Tarantula Survey (VFTS; Evans et al. 2011). Ex-cluding stars with log T e ff [K] < Article number, page 3 of 19 & A proofs: manuscript no. AA_2020_4_ncastro_astroph as possible emission-line stars with unreliable temperatures fromour approach; see Sect. 4.2), there are 42 stars in common.Table 1 compares our results with those obtained fromthe relevant VFTS studies (Sabín-Sanjulián et al. 2014, 2017;McEvoy et al. 2015; Ramírez-Agudelo et al. 2017; Garland et al.2017; Schneider et al. 2018b). The VFTS stellar parameterswere also determined using standard techniques and the fast - wind stellar atmosphere code . Within the uncertainties, thereis reasonably good agreement between the estimated tempera-tures (Fig. 2), albeit with some significant outliers at the highestvalues. We find a good match, with some outliers, between theluminosities estimated in this work (see Sect. 5.2) and VFTS re-sults as well.However, there is a large scatter between the estimated sur-face gravities (Fig. 2), with the MUSE estimates systematically ∼ ff er significantly and which have strong neb-ular contamination. MUSE 1297 (VFTS 493) shows a remark-ably large discrepancy in the gravity ( ∼ β continuum,due to the spectral resolution and strong nebular contamination,could be behind the discrepancy. We analysed the three VFTSstars in Fig. 3 using the grid described in this work and the bluewavelengths available in the VFTS spectra, that is, including the ∼ − ff erences in these threestars (see Table 1) by ∼ . We used a sample of stars available in both the MUSE data andthe VFTS to investigate the use of the He i λ ii λ = i / He ii )] + . The typical un-certainty for a given equivalent-width ratio is of the order of ± ffi cient for the sort of exploratorystudies undertaken with MUSE. We find a similar trend to thatreported by Kerton et al. (1999) for Galactic O stars. In partic-ular, their results over the range − < [log(He i / He ii )] < With the exception of the study from Garland et al. (2017), who used tlusty model atmospheres (Hubeny & Lanz 1995). SpT: O2 = =
9, B0 = = We measured the He i / He ii ratio of the full MUSE sampleand used these to estimate spectral types, as listed in Table 2.Figure 5 compares the T e ff estimates with the classificationsobtained from the He i / He ii ratio (again excluding those withlog T e ff [K] < ff ects at this point (see Fig. 4). Not unexpectedly, the largestdiscrepancies with the linear trend are found at the extremes ofthe distribution where the diagnostic lines become very weak orabsent (i.e. He ii λ ii λ
4. Evolutionary status of NGC 2070
The sHRD for the MUSE sample is shown in Fig. 6 and canbe described by two groups. The largest fraction (281 of 333stars) is located in the region of the main sequence predicted bythe evolutionary models, accounting for the e ff ects of rotationfrom Köhler et al. (2015). There are two distinctive populationsin the main sequence, as highlighted by the right-hand panel ofFig. 6, which shows the summed probability distributions fromthe analysis of each star along the entire fastwind grid (see Cas-tro et al. 2018b). The remaining 52 stars appear to lie beyond thetheoretical TAMS at log T e ff [K] < Figure 6 suggests two subgroups within the main sequence sam-ple, which may reflect di ff erent bursts of star-formation in theregion (e.g. Cignoni et al. 2015, and also Sect. 5.1). He ii λ e ff [K] ∼ e ff [K] > / or binary evolution products (Wang et al. 2020). However,these stars also have large uncertainties in their parameters asthey are constrained only by He ii and H β and the non-detectionof He i lines.Given that star formation is still underway in NGC 2070(Walborn et al. 1999, 2013), we would have expected to find alarger population close to the expected ZAMS. The lack of mas-sive ( >
30 M (cid:12) ) O-type stars close to the ZAMS has previouslybeen noted in the Milky Way (Castro et al. 2014; Holgado et al.2018, 2020) and in the SMC (Lamb et al. 2013; Castro et al.2018b). It was suggested that very young stars may still be em-bedded in their natal clouds and thus not accessible for opticalobservations. However, Kennicutt (1984) has shown that the em-bedded phase is expected to be relatively short (10% of the typ-ical ∼ ii λ ii λ Article number, page 4 of 19. Castro et al.: The sHRD of OB stars in NGC 2070
Fig. 3.
Comparison between three stars analysed in this work (solid black line) and in the VFTS project (solid blue line) whose derived gravitiesdi ff er significantly between studies. The best fastwind model obtained in the MUSE analysis is shown (solid red lines). Wavelengths expected tobe strongly a ff ected by nebular contamination are marked in grey. Fig. 4.
Spectral type calibration (solid red line) from fitting theHe i λ / He ii λ i λ / He ii λ Further down the main sequence, we find 134 late O-type andearly B-type stars with typical temperatures of log T e ff [K] ∼ i lines dominate the spectrum; weak He ii λ Fig. 5.
Estimated e ff ective temperatures (T e ff ) of the MUSE stars ver-sus their spectral types from the calibration in Fig. 4. For clarity, thestars have been artificially distributed into (continuous) spectral typesto avoid significant overlap. The distribution is colour-coded by surfacegravity (see Table 2). absorption in a couple of cases indicates that they are on the cuspof the O-B transition at the very earliest B-types. These stars arestill too young to have reached the TAMS and cannot serve as re-liable anchors such as those proposed in the Milky Way (Castroet al. 2014) and the SMC (Castro et al. 2018b). Article number, page 5 of 19 & A proofs: manuscript no. AA_2020_4_ncastro_astroph
Table 1.
Estimated e ff ective temperatures, surface gravities, and luminosities from MUSE (cf. published values from the VFTS). MUSE VFTS MUSE VFTS MUSE VFTST e ff σ T e ff T e ff σ T e ff log g σ log g log g σ log g log L σ log L log L σ log L MUSE ID VFTS ID (K) (K) (K) (K) (dex) (dex) (dex) (dex) [ L (cid:12) ] [ L (cid:12) ] [ L (cid:12) ] [ L (cid:12) ]830 465 59000 13500 39050 820 4.0 0.4 3.77 0.10 6.023 0.127 5.57 0.101068 518 55000 11700 44850 500 4.0 0.4 3.67 0.10 5.989 0.403 5.67 0.102901 382 47000 11400 40000 1500 4.0 0.3 3.81 0.10 5.329 0.199 5.31 0.132451 385 47000 7200 42900 1700 3.8 0.2 3.87 0.10 5.559 0.120 5.55 0.291008 511 42000 1000 43700 1700 4.0 0.1 4.25 0.11 5.365 0.049 5.46 0.151699 667 41000 1000 38750 820 3.9 0.1 3.59 0.10 5.284 0.050 5.21 0.101433 599 40000 4500 47300 500 3.6 0.1 4.02 0.10 5.783 0.066 6.01 0.101890 601 40000 1000 40280 500 3.8 0.1 3.94 0.10 5.495 0.046 5.55 0.18276 491 39000 1400 40360 800 3.6 0.2 3.84 0.10 5.415 0.049 5.43 0.162780 648 39000 1000 40000 1500 3.6 0.1 3.80 0.10 5.607 0.049 5.66 0.13955 536 39000 1400 41500 1540 4.0 0.2 4.23 0.15 5.124 0.048 5.19 0.17195 494 37000 1200 38940 1740 3.8 0.2 4.21 0.21 4.993 0.046 5.03 0.202385 456 36000 12400 35850 640 3.4 0.4 3.93 0.10 5.117 0.063 5.17 0.103081 484 36000 1200 35680 680 3.4 0.1 3.68 0.10 5.276 0.046 5.41 0.143200 564 36000 1800 37000 1500 4.1 0.4 4.10 0.10 4.818 0.047 5.33 0.131870 611 35000 1700 37410 900 3.6 0.3 4.13 0.14 4.724 0.047 4.79 0.142223 436 35000 1900 35000 1500 3.8 0.4 3.90 0.10 4.463 0.049 4.87 0.132897 419 34000 1000 33100 900 3.6 0.2 3.64 0.10 5.040 0.046 5.07 0.24774 664 34000 1200 35700 500 3.2 0.1 3.58 0.10 5.500 0.170 5.53 0.10375 597 34000 1000 35400 720 3.6 0.1 3.94 0.11 4.826 0.047 4.87 0.142985 571 33000 1300 31100 770 4.1 0.3 4.31 0.10 4.383 0.048 4.39 0.101297 493 33000 2600 37050 950 3.3 0.5 4.27 0.10 4.112 0.061 5.06 0.163172 609 33000 2200 33000 1500 3.9 0.5 3.82 0.10 4.401 0.047 4.52 0.13911 498 33000 1000 33230 810 3.9 0.2 4.12 0.15 4.813 0.049 4.88 0.141334 635 32000 1600 34120 500 3.5 0.3 4.00 0.10 4.877 0.046 4.83 0.121387 592 32000 1800 33560 1000 4.0 0.3 4.28 0.13 4.550 0.063 4.69 0.132038 649 32000 1500 34750 630 3.6 0.2 4.19 0.10 4.607 0.047 4.71 0.122256 393 32000 1200 31600 500 3.5 0.2 3.55 0.10 4.882 0.048 4.92 0.103027 660 32000 1400 32260 1020 3.8 0.2 4.15 0.16 4.708 0.047 4.73 0.20710 560 31000 1900 33570 1150 3.6 0.4 4.20 0.16 4.475 0.047 4.52 0.182815 620 31000 2700 31700 830 3.8 0.4 4.11 0.10 4.581 0.061 4.31 0.102114 607 30000 1900 32800 560 3.6 0.3 4.23 0.10 4.437 0.059 4.56 0.101826 624 30000 1500 29000 1080 3.8 0.3 4.00 0.44 4.348 0.061 4.20 0.102939 554 30000 2900 34130 770 3.7 0.5 4.30 0.10 4.256 0.082 4.51 0.101894 659 28000 1600 30000 1920 3.5 0.2 4.30 0.10 4.473 0.060 4.55 0.11888 612 28000 2200 27000 1000 3.7 0.2 4.30 0.10 4.481 0.077 4.48 0.103018 449 28000 13500 24000 1000 3.8 1.2 3.80 0.10 3.964 0.184 3.87 0.102804 575 26000 2100 26000 1000 3.3 0.2 3.75 0.20 4.704 0.062 – –1951 646 25000 1600 24000 1000 2.6 0.1 2.80 0.10 4.853 0.160 4.77 0.101689 420 25000 2100 26500 1000 2.6 0.2 3.00 0.20 5.812 0.194 5.84 0.102190 590 23000 1100 24000 1000 2.5 0.1 2.80 0.20 5.786 0.150 5.87 0.101399 417 21000 4500 18500 1000 2.7 0.5 2.55 0.20 4.822 0.160 4.51 0.20 Notes.
Columns 1 and 2: MUSE and VFTS identifications (Paper I and Evans et al. 2011, respectively). Columns 3-6: E ff ective temperatures (anduncertainties) from MUSE and published studies from the VFTS (Sabín-Sanjulián et al. 2014, 2017; McEvoy et al. 2015; Ramírez-Agudelo et al.2017; Garland et al. 2017; Schneider et al. 2018b). Columns 7-10: Same, but for surface gravities. Columns 11-14: Same, but for luminosities. The region of the sHRD in Fig. 6 where we would expect tofind B-type supergiants (log T e ff [K] ∼ .
1, log L / L (cid:12) > .
0) in-cludes several stars, matching the extended main sequence pre-dicted by Köhler et al. (2015). The extension of the empiricalTAMS in the upper part of the sHRD suggests a possible enve-lope inflation scenario (see Sanyal et al. 2015, 2017). However,given the young age of NGC 2070, the sample of presumed su-pergiants in the MUSE data is too small to provide robust testsof these predictions. We add that our results place these stars atthe edge of the model grid, and as such additional analysis iswarranted.
We find 52 stars (including the B-type supergiants) withlog T e ff [K] < .
3, thus placing them beyond the TAMS predictedby the models of Köhler et al. (2015). The spectra of four exam-ples of this group are shown in Fig. 9. Once stars start burningHe in their cores, theoretical evolutionary tracks predict a rapidevolution until they expand and cool to reach the red supergiant(RSG) phase. The position of these objects between the main se-quence and the RSG phase is therefore puzzling and not in agree-ment with the expected evolution of a single star, unless they are
Article number, page 6 of 19. Castro et al.: The sHRD of OB stars in NGC 2070
Fig. 6.
Spectroscopic HRD (sHRD, L ≡ T ff / g , Langer & Kudritzki 2014) for the MUSE sample. Left: Positions of the MUSE sample in thesHRD (red and blue dots, o ff set slightly where required to avoid overlap) compared to the equivalent probability distribution (PD) for the MilkyWay from Castro et al. (2014, grey shaded regions) and theoretical rotating evolutionary tracks from Köhler et al. (2015). Stars apparently beyondthe TAMS, flagged as candidate emission-line stars (Castro et al. 2018b), are marked in blue in the left-hand panel (see Sect. 4.2). Right:
SummedPD functions from the MUSE analysis and the same evolutionary tracks, in which the blue dots indicate equal time steps of 0.1 Myr. Horizontallines at log L / L (cid:12) = L / L (cid:12) = blue-loop objects in a post-RSG phase (e.g. Schootemeijer et al.2019).The sHRD for the Milky Way from Castro et al. (2014) alsofound stars in this range (log T e ff [K] ≈ β , although[O iii ] emission is also seen, suggesting that the H β emissionis, at least in part, due to nebular contamination. In contrast tothe Castro et al. (2018b) study, here we cannot disentangle neb-ular contamination from any other contribution in the H β andH α emission lines. We also note that two objects in Fig. 9 showweak He ii λ ii λ
5. Discussion
The two well-populated parts of the main sequence in the sHRD(Fig. 6) suggest two di ff erent stages of star formation in therecent history of NGC 2070. E ff ective temperatures and gravi-ties, resulting from the spectral atmosphere analyses, were com-pared to the LMC evolutionary tracks from Köhler et al. (2015).Masses and ages were calculated by interpolating the tracks fromKöhler et al. at each target’s sHRD location as marked by ourresults for e ff ective temperatures and gravities, using SciPy li- braries . Ages are shown in the left-hand panel of Fig 10; starswith estimated parameters outside the evolutionary tracks werenot considered further at this point. We found an average agefor the O-type main sequence stars of 2.1 ± e ff [K] ∼ ± ff ectthe ages extracted from the sHRD. We tested increasing the grav-ities by 0.3 dex (see Sect. 3.1), finding a similar distribution inagreement, within the errors, with the bi-modal age distributionpresented in Fig 10. As shown in the right-hand panel of Fig. 10,the younger stars are more clustered around R136. However,there is no clear age segregation in NGC 2070. Older ages seemto be placed in the outskirts of the cluster; however, the num-ber of analysed stars in these regions is lower than in the core(Fig. 1), which may be the result of a statistical bias. The distribution of the MUSE sample in the HRD is shown in theleft-hand panel of Fig. 11. Stellar luminosities were calculatedusing the relevant photometry provided in Paper I (aside fromthe 13 stars marked with ’*’ in Table 2) and adopting a distanceto the LMC of 49.9 kpc (Pietrzy´nski et al. 2013). Flux-calibratedMUSE spectra for each individual star were compared to the re-spective synthetic fastwind spectral energy distributions (SEDs),obtained from the stellar atmosphere analysis and parameters inTable 2. We estimated stellar radii and colour excesses, E ( B − V ),that provide the best match between the observed and syntheticSEDs. We adopted an extinction law Rv = Av / E ( B − V ) = https: // docs.scipy.org / doc / scipy / reference / interpolate.htmlArticle number, page 7 of 19 & A proofs: manuscript no. AA_2020_4_ncastro_astroph
Fig. 7.
Examples of model fits to four O-type main sequence stars. Areas strongly a ff ected by nebular contamination are marked in grey. Spectraltypes based on He i λ ii λ i λ ii λ Fig. 8.
Example of model fits to four early B-type main sequence stars (see Fig. 7).Article number, page 8 of 19. Castro et al.: The sHRD of OB stars in NGC 2070
Fig. 9.
Examples of model fits to four stars apparently beyond the TAMS from the model-atmosphere analysis but which we suspect are emission-line objects and / or contaminated by significant nebular emission (regions marked in grey), such that the estimated temperatures are unreliable (seeSect. 4.2 and Castro et al. 2018b). Fig. 10.
Distribution of inferred ages from the location of stars (log T e ff [K] > ff erent colours. Right:
Spatial distribution of the sample,in which each hexabin shows the mean age value of all stars within it. stars in the main sequence, but there are di ff erences for the mostmassive stars in the upper part of the diagram. Those beyond theTAMS in the sHRD are systematically shifted to lower luminosi-ties and masses in the HRD. Due to the concern regarding thederived temperatures, stars at log T e ff [K] < Article number, page 9 of 19 & A proofs: manuscript no. AA_2020_4_ncastro_astroph son. At the high-mass end ( M (cid:38) M (cid:12) ), the masses estimatedfrom the sHRD are significantly larger than the ones from theHRD, as shown in the right-hand panel of Fig. 11. These di ff er-ences may be linked to the long-standing discrepancy betweenspectroscopic and evolutionary mass estimates for massive stars(e.g. Herrero et al. 1992; Weidner & Vink 2010; Markova &Puls 2015). A similar result was found from an analysis of thewider 30 Dor population of O-type stars by Sabín-Sanjulián et al.(2017). When using the Kiel diagram (log T e ff [K] and log g ) toestimate masses of similar stars in the Milky Way, they were alsofound to be larger than those from the HRD at the high-mass end(Markova et al. 2018). A similar trend was found for the mostmassive stars in the SMC by Castro et al. (2018b).The uncertainty in the gravities from the MUSE data(Sect. 3.1) and stellar wind constraints in the grid could havecontributed to the mass di ff erences: If the surface gravity is in-correct, simultaneously fitting T e ff and gravity can lead to un-derestimates of T e ff (e.g. Schneider et al. 2017). The systematicdi ff erence of approximately 0.3 dex found for the stars presentin both the VFTS and MUSE data could somewhat alleviate thisdiscrepancy. That said, as similar mass discrepancies are seenin other studies (using di ff erent observations, algorithms, atmo-spheric models, etc.) it seems unlikely that this is simply an arte-fact of the MUSE analysis. We are now exploring alternativeroutes to improve the estimates of stellar gravities from MUSEdata, such as using absorption lines from the hydrogen Paschenseries (Bestenlehner et al. in prep.). The distribution of estimated v sin i values is shown in theleft-hand panel of Fig. 12. There is a peak at approximately170 km s − for the full sample, with no clear qualitative di ff er-ences for the stars separated into the two age groups in the mainsequence. Their overall distribution resembles the Ramírez-Agudelo et al. (2013) results for the O-type stars in 30 Dorrather than the Dufton et al. (2013) bi-modal distribution forlower-mass B-type stars. The peak of the hot O-type star group(log T e ff [K] ∼ .
6) also resembles the rotational velocity dis-tribution found in Cygnus OB2 in the Milky Way by Berlanaset al. (2020). There is a relative dearth of slow rotators in thecooler MUSE group, but we caution that the spectral resolutionof MUSE limits us to ∆ v sin i ∼
60 km s − , and as such we arenot able to robustly probe the low-velocity end of the distribu-tion. We note that Kamann et al. (2020) have recently measuredrotational velocities for a total of 1400 stars of the intermediateage cluster NGC1846 in the LMC with uncertainties of typically10 km / s using MUSE. A future, more refined analysis may allowus to investigate these results in more detail.There appears to be a prolongation in the distribution at v sin i ∼
370 km s − for the hot O-type stars (see Fig. 12), whichresembles the high-velocity tail found for apparent single O-typestars in 30 Dor by Ramírez-Agudelo et al. (2013). de Mink et al.(2013) proposed that rapidly rotating stars may originate frombinary interactions and mergers (de Mink et al. 2014; Schneideret al. 2016). These stars in the MUSE sample merit further ob-servations to test if these objects are actually single stars as wellas to investigate their physical properties in more detail relativeto the interaction and merger models. As shown in the right-handpanel of Fig. 12, there do not appear to be strong trends in the v sin i estimates or their location in the sHRD.
6. Summary
Exploiting the unique observational capabilities of MUSE,combined with synthetic spectra calculated with fastwind , wehave estimated physical parameters for 333 OB-type stars inNGC 2070. The majority of these objects are analysed for thefirst time here. Our main conclusions can be summarised as fol-lows. –
281 stars (84% of our sample) are still in the main sequence.They comprise a group of O-type stars with an average ageof 2.1 ± ± – We find a relative dearth of O-type stars close to the theoret-ical ZAMS between approximately 20 and 50 M (cid:12) . Similarfindings were reported in the the Milky Way and the SMC(Holgado et al. 2018, 2020; Castro et al. 2018b). Given theyoung age of NGC 2070, this is somewhat unexpected, al-though stars in R136 are omitted from our sample. The stellarcontext of R136 needs to be better quantified before furtherconclusions can be reached (see Bestenlehner et al. 2020).Moreover, the stars close to the theoretical ZAMS, in the up-per part of the sHRD ( >
50 M (cid:12) ), match the predicted po-sition of stellar mergers (Schneider et al. 2016) and / or bi-nary evolution products (e.g. Wang et al. 2020). However,the temperatures for these stars have large uncertainties, andfurther studies of their properties are also required. – We find 52 stars, the rest of the analysed sample, with tem-peratures beyond the theoretical TAMS from Köhler et al.(2015) at log T e ff [K] < / or nebular contam-ination, where the analysis tools give incorrect results giventhe limitations of the data and the atmospheric models, butwe need further observations to test this suggestion. – The HRD and sHRD are in good qualitative agreement forthe late O-type and early B-type stars in the main sequence,but there are di ff erences for the more massive O-type stars.Masses estimated from the sHRD compared to the evolution-ary tracks are larger than those inferred from the HRD, whichbecomes severe (a factor of two to three) at M > M (cid:12) . Thismay be related to the uncertainty in the surface gravities es-timated from the MUSE data (Sect 3.1). However, Sabín-Sanjulián et al. (2017) found similar problems at M > M (cid:12) in 30 Dor, and a comparable trend was also found by Cas-tro et al. (2018b) in the SMC (from observations of the moreclassical blue-visible range, albeit still at R ∼ – The projected v sin i distribution for the MUSE samplepeaks at 170 km s − . We find a group of rapidly rotating O-type stars (with 300 < v sin i <
450 km s − ) that resembles thehigh-velocity tail found for the wider population of O starsin 30 Dor by Ramírez-Agudelo et al. (2013). Comparisonsof our results with the bi-modal distribution for the B-typestars from Dufton et al. (2013) are unfortunately limited bythe velocity resolution of the MUSE data. – We used the He i λ / He ii λ ff ective temperatures estimated from the model-atmospherefits follow a clear trend of decreasing temperature towardslate spectral types. Article number, page 10 of 19. Castro et al.: The sHRD of OB stars in NGC 2070
Fig. 11.
HRD for the MUSE sample with log T e ff [K] > Right: sHRD ( L ≡ T ff / g , Langer & Kudritzki 2014) for the sampleindicating the di ff erence in inferred mass between the sHRD and HRD approaches; each hexabin shows the mean value of all stars within it.Evolutionary tracks in both plots are those from Köhler et al. (2015). Stars outside of the evolutionary tracks are not included in the mass analysis. Fig. 12.
Distribution of projected rotational velocities ( v sin i ) for the two samples identified in the main sequence (left panel). Right: sHRD( L ≡ T ff / g ) for the total sample, with v sin i average in each bin, and overlaid on the rotating evolutionary tracks from Köhler et al. (2015). Eachhexabin shows the mean value of all stars within it. The next step beyond the current sample is analysis of the W-R and other He ii emission-line stars in NGC 2070 to completethe distribution in the sHRD. Additional analyses to improve thequoted surface gravities and overcome the limitations of basingthe stellar gravity on H β are also desirable. We are exploring thePaschen lines as possible additional constraints for the gravity(Bestenlehner in prep.). Furthermore, as with the rapidly rotat-ing O-type stars identified by Ramírez-Agudelo et al. (2013), thecomparable group from the MUSE data (Fig. 12) are interestingin the context of possible post-interaction or merger products,and multi-epoch spectroscopy of this subgroup would be partic-ularly valuable. As shown by Giesers et al. (2019), multi-epochMUSE observations are indeed uniquely capable of detectingspectroscopic binaries in star clusters.Finally, we note that the commissioning of the MUSENarrow-Field Mode with adaptive optics support has added a new capability for integral field spectroscopy from the groundwith angular resolution close to that from the Hubble Space Tele-scope. We have already secured data for NGC2070 in this modeand will soon report on results in the most crowded regions ofR136 (Castro et al. 2021).In conclusion, integral field spectroscopy with MUSE hasbeen demonstrated to be a powerful tool for the quantitativespectroscopy of stars in crowded fields. Studies of this kind haveonly begun to scratch the surface of what is expected to be-come an indispensable tool, in particular in view of the upcom-ing generation of extremely large telescopes and the next genera-tion of integral field spectrographs (e.g. the BlueMUSE concept;Richard et al. 2019). Acknowledgements.
The authors thank the referee for useful comments andhelpful suggestions that improved this manuscript. NC gratefully acknowledgefunding from the Deutsche Forschungsgemeinschaft (DFG) - CA 2551 / Article number, page 11 of 19 & A proofs: manuscript no. AA_2020_4_ncastro_astroph terio de Ciencia e Innovación through grants PGC-2018-091 3741-B-C22 andCEX2019-000920-S, and from the Canarian Agency for Research, Innovationand Information Society (ACIISI), of the Canary Islands Government, and theEuropean Regional Development Fund (ERDF), under grant with referenceProID2020010016. Our research used Astropy, a community-developed corePython package for Astronomy (Astropy Collaboration et al. 2013), and APLpy,an open-source plotting package for Python (Robitaille & Bressert 2012).
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Article number, page 12 of 19. Castro et al.: The sHRD of OB stars in NGC 2070 T a b l e . E s ti m a t e dphy s i ca l p a r a m e t e r s o f t h e ea r l y - t yp e s t a r s w it h l og T e ff [ K ] > . i n NG C fr o m t h e M U S E ob s e r v a ti on ss o r t e dby e ff ec ti v e t e m p e r a t u r e . S ee S ec t . f o r a d e s c r i p ti ono f t h ea n a l y s i s a nd li m it a ti on s i n t h e li s t e dp a r a m e t e r s . C o l u m n s - : I d e n ti fi ca ti on a nd c oo r d i n a t e s fr o m C a s t r o e t a l . ( a ) . C o l u m n s - : E s ti m a t e d e ff ec ti v e t e m p e r a t u r e s , s p ec t r o s c op i c l u m i no s iti e s ( L ≡ T e ff / g , L a ng e r & K ud r it z k i ) , l u m i no s iti e s ( L ) , a nd t h e i r un ce r t a i n ti e s . T h e p r ob a b ilit yd i s t r i bu ti on s f o r s t a r s i n t h e upp e r p a r t o f t h e s H R D , c l o s e t o t h ee dg e o f t h e g r i d ( a pp r ox i m a t e l y l og L / L (cid:12) > . ) , dono t p r ov i d ee nough i n f o r m a ti on t op r op e r l y e s ti m a t e un ce r t a i n ti e s , a nd t h e v a l u e s c it e d i n t h i s t a b l e m u s t b ec on s i d e r e d a s r ough e s ti m a ti on s . C o l u m n s - : E x ti n c ti on a ndv i s u a l m a gn it ud e s . T h i r t ee n s t a r s i n c l ud e d i n t h i s w o r k w e r e no tli s t e d i n C a s t r o e t a l . ( a ) . T h e s e s t a r s a r e m a r k e dby a ’ * ’ a f t e r t h e i r m a gn it ud e s . C o l u m n s - : M a ss e s e s ti m a t e d fr o m t h e s H R D a nd H R D , r e s p ec ti v e l y . C o l u m n14 : A g e s e s ti m a t e d fr o m po s iti on s i n t h e s H R D . C o l u m n15 : E s ti m a t e s o f p r o j ec t e d r o t a ti on a l v e l o c iti e s ( v s i n i )fr o m t h e s p ec t r a l fi tti ng . C o l u m n16 : S p ec t r a lt yp e s d e r i v e d acc o r d i ng t o t h e H e i λ t o H e ii λ r a ti o . M a ss e s a nd a g e s a r ee s ti m a t e d fr o m c o m p a r i s on s w it h e vo l u ti on a r y m od e l s fr o m K öh l e r e t a l . ( ) . S t a r s ou t s i d e o f t h ee vo l u ti on a r y t r ac kbound a r i e s a r e no t c on s i d e r e d i n t h ea n a l y s i s (’ – ’) . M U S E I D α ( J ) δ ( J ) l og T e ff σ l og T e ff l og L σ l og L l og L σ l og L A v V M a ss L M a ss L A g e L v s i n i S p T [ h , m , s ][ ◦ , (cid:48) , (cid:48)(cid:48) ][ K ][ K ][ L (cid:12) ][ L (cid:12) ][ L (cid:12) ][ L (cid:12) ][ m a g ][ m a g ][ M (cid:12) ][ M (cid:12) ][ M y r][ k m s − ] : : . - : : . . . . . . . . . O : : . - : : . . . . . . . . . O : : . - : : . . . . . . . . . O : : . - : : . . . . . . . . . O : : . - : : . . . . . . . . . O : : . - : : . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O Article number, page 13 of 19 & A proofs: manuscript no. AA_2020_4_ncastro_astroph T a b l e . C on ti nu e d . M U S E I D α ( J ) δ ( J ) l og T e ff σ l og T e ff l og L σ l og L l og L σ l og L A v V M a ss L M a ss L A g e L v s i n i S p T [ h , m , s ][ ◦ , (cid:48) , (cid:48)(cid:48) ][ K ][ K ][ L (cid:12) ][ L (cid:12) ][ L (cid:12) ][ L (cid:12) ][ m a g ][ m a g ][ M (cid:12) ][ M (cid:12) ][ M y r][ k m s − ] : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . O : : . - : : . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O Article number, page 14 of 19. Castro et al.: The sHRD of OB stars in NGC 2070 T a b l e . C on ti nu e d . M U S E I D α ( J ) δ ( J ) l og T e ff σ l og T e ff l og L σ l og L l og L σ l og L A v V M a ss L M a ss L A g e L v s i n i S p T [ h , m , s ][ ◦ , (cid:48) , (cid:48)(cid:48) ][ K ][ K ][ L (cid:12) ][ L (cid:12) ][ L (cid:12) ][ L (cid:12) ][ m a g ][ m a g ][ M (cid:12) ][ M (cid:12) ][ M y r][ k m s − ] : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O Article number, page 15 of 19 & A proofs: manuscript no. AA_2020_4_ncastro_astroph T a b l e . C on ti nu e d . M U S E I D α ( J ) δ ( J ) l og T e ff σ l og T e ff l og L σ l og L l og L σ l og L A v V M a ss L M a ss L A g e L v s i n i S p T [ h , m , s ][ ◦ , (cid:48) , (cid:48)(cid:48) ][ K ][ K ][ L (cid:12) ][ L (cid:12) ][ L (cid:12) ][ L (cid:12) ][ m a g ][ m a g ][ M (cid:12) ][ M (cid:12) ][ M y r][ k m s − ] : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . O : : . - : : . . . . . . . . . . B : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . B : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . O Article number, page 16 of 19. Castro et al.: The sHRD of OB stars in NGC 2070 T a b l e . C on ti nu e d . M U S E I D α ( J ) δ ( J ) l og T e ff σ l og T e ff l og L σ l og L l og L σ l og L A v V M a ss L M a ss L A g e L v s i n i S p T [ h , m , s ][ ◦ , (cid:48) , (cid:48)(cid:48) ][ K ][ K ][ L (cid:12) ][ L (cid:12) ][ L (cid:12) ][ L (cid:12) ][ m a g ][ m a g ][ M (cid:12) ][ M (cid:12) ][ M y r][ k m s − ] : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . B : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . B : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . B : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . B : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . B : : . - : : . . . . . . . . . . B : : . - : : . . . . . . . . . . B : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . B : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . B : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . B : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . B : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . B Article number, page 17 of 19 & A proofs: manuscript no. AA_2020_4_ncastro_astroph T a b l e . C on ti nu e d . M U S E I D α ( J ) δ ( J ) l og T e ff σ l og T e ff l og L σ l og L l og L σ l og L A v V M a ss L M a ss L A g e L v s i n i S p T [ h , m , s ][ ◦ , (cid:48) , (cid:48)(cid:48) ][ K ][ K ][ L (cid:12) ][ L (cid:12) ][ L (cid:12) ][ L (cid:12) ][ m a g ][ m a g ][ M (cid:12) ][ M (cid:12) ][ M y r][ k m s − ] : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . B : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . B : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . B : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . O : : . - : : . . . . . . . . . . B : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . B : : . - : : . . . . . . . . . . B : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . B : : . - : : . . . . . . . . . . B : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . B : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . B : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . B : : . - : : . . . . . . . . . . B : : . - : : . . . . . . . . . . B : : . - : : . . . . . . . . . . B : : . - : : . . . . . . . . . . B : : . - : : . . . . . . . . . . B : : . - : : . . . . . . . . . . B : : . - : : . . . . . . . . . . B : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . B Article number, page 18 of 19. Castro et al.: The sHRD of OB stars in NGC 2070 T a b l e . C on ti nu e d . M U S E I D α ( J ) δ ( J ) l og T e ff σ l og T e ff l og L σ l og L l og L σ l og L A v V M a ss L M a ss L A g e L v s i n i S p T [ h , m , s ][ ◦ , (cid:48) , (cid:48)(cid:48) ][ K ][ K ][ L (cid:12) ][ L (cid:12) ][ L (cid:12) ][ L (cid:12) ][ m a g ][ m a g ][ M (cid:12) ][ M (cid:12) ][ M y r][ k m s − ] : : . - : : . . . . . . . . . . B : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . B : : . - : : . . . . . . . . . . B : : . - : : . . . . . . . . . . B : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . B : : . - : : . . . . . . . . . . B : : . - : : . . . . . . . . . . B : : . - : : . . . . . . . . . . B : : . - : : . . . . . . . . . . B : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . B : : - : : . . . . . . . . . . B : : . - : : . . . . . . . . . . B : : . - : : . . . . . . . . . . B : : . - : : . . . . . . . . . . B : : . - : : . . . . . . . . . . O : : . - : : . . . . . . . . . . B : : . - : : . . . . . . . . . . B : : . - : : . . . . . . . . . . B : : . - : : . . . . . . . . . . B : : . - : : . . . . . . . . . . B : : . - : : . . . . . . . . . . O9