sign in sign up
<<
Home , Large Magellanic Cloud, Local Group, NGC 2070, R136a3, Tarantula Nebula

Astronomical Science DOI: 10.18727/0722-6691/5223

Mapping the Youngest and Most Massive in the Tarantula with MUSE-NFM

Norberto Castro 1 Myrs, but in very dramatic ways. The are to unveil the of the most mas- Martin M. Roth 1 energy released during their short lives, sive stars, to constrain the role of these Peter M. Weilbacher 1 and their deaths in explosions, parameters in their evolution, and to pro- Genoveva Micheva 1 shape the chemistry and dynamics of vide homogeneous results and landmarks Ana Monreal-Ibero 2, 3 their host . Ever since the reioni- for the theory. Spectroscopic surveys Andreas Kelz1 sation of the , massive stars have transformed the field in this direc- Sebastian Kamann4 have been significant sources of ionisa- tion, yielding large samples for detailed Michael V. Maseda 5 tion. Nonetheless, the evolution of mas- quantitative studies in the (for Martin Wendt 6 sive O- and B-type stars is far from being example, Simón-Díaz et al., 2017) and in and the MUSE collaboration well understood, a lack of knowledge that the nearby (for exam- is even worse for the most massive stars ple, Evans et al., 2011). However, massive (Langer, 2012). These missing pieces in stars are rarer than smaller stars, and 1 Leibniz-Institut für Astrophysik Potsdam, our understanding of the formation and very massive stars (> 70 M☉) are even Germany evolution of massive stars propagate to rarer. The empirical distribution of stars 2 Instituto de Astrofísica de Canarias, other fields in astrophysics. Supernova on the upper part of the Hertzsprung-­ La Laguna, Tenerife, Spain rates, ionisation radiation, and chemical Russell (HR) diagram remains questiona- 3 Departamento de Astrofísica, yields will depend on the evolutionary ble and more data are essential. Universidad de La Laguna, Tenerife, paths of massive stars. Ultimately, under- Spain standing the evolution of -forming gal- The heart of the (NGC 4 Astrophysics Research Institute, axies depends first and foremost on our 2070) in the Liverpool John Moores University, UK ability to constrain the evolution of mas- (LMC) is intrinsically the brightest 5 Leiden Observatory, Leiden University, sive stars. the Netherlands 6 Institut für Physik und Astronomie, is mainly governed by Figure 1. Colour-composite mosaic (RGB: I, R and V filters) of nine of the fields observed with MUSE-NFM Universität Potsdam, Germany the initial . Nevertheless, other fac- in the core of NGC 2070. Image quality ranges tors can play a significant role. Metallicity, between 50 and 80 milliarcseconds, akin to the spa- rotational velocity, duplicity or strong stel- tial resolution of the HST. The HST image in the The evolution of the most massive stars lar winds affect their lifetimes (Maeder & F555W band (Sabbi et al., 2013) is displayed in the background. The inset image is a zoom into the core is a puzzle with many missing pieces. Meynet, 2000; Langer, 2012). Large of (marked by a circle in the mosaic) resolving Statistical analyses are key to providing systematic surveys are fundamental if we , 2 and 3 WR stars. anchors to calibrate theory, but per- forming these studies is an arduous job. The state-of-the-art integral field spec- trograph Multi Unit Spectroscopic Explorer (MUSE) has stirred up stellar R136a1 astrophysicists, who are excited about R136a2 its ability to take spectra of up to a thousand stars in a single exposure. N 1 arcsecond The excitement was even greater E with the commissioning of the MUSE narrow-­field mode (MUSE-NFM) that has demonstrated angular resolution akin to that of the (HST). We present the first mapping of the dense stellar core R136 in the Tarantula nebula based on a MUSE-NFM mosaic. We aim to deliver the first homogeneous analysis of the most massive stars in the local Universe and to explore the impact of these peculiar objects on the (ISM).

N Resolving the heart of NGC 2070 with MUSE-NFM 7.5 arcseconds The evolution of the Universe is tied to E massive stars. They live fast, only a few

50 The Messenger 182 | 2021 1e–14 Figure 2. Representative OB stars extracted from the 1.0 Teff = 46 000 (K) central field of the R136 cluster (blue). The stars were 0.8 modelled (orange) with a dedicated FASTWIND grid (Puls et al., 2005). The and key diagnostic lines are also indicated. The areas that 4800 4900 5000 5100 5200 5300 5400 5500 1e–15 could be affected by the sky subtraction are high- 1.5 Teff = 39 000 (K) lighted (grey shading).

1.0 MUSE-NFM and mosaicked the R136 –1

Å 4800 4900 5000 5100 5200 5300 5400 5500

2 1e–15 cluster from a total of nine pointings. The 1.5 Teff = 36 000 (K)

cm tenth one was centred on the Wolf-Rayet

–1 (WR) system R140. The outstanding per- s I I I II

1.0 III] III] β rg H He He He [O [O He formance of MUSE-NFM and its associ-

(e 4800 4900 5000 5100 5200 5300 5400 5500 ated Ground Atmospheric Layer Adaptive 1e–15

Flux optiCs for Spectroscopic Imaging Teff = 23 000 (K) 2.0 (GALACSI) module in combination with 1.5 the Adaptive Optics Facility of the VLT 4800 4900 5000 5100 5200 5300 5400 5500 provides a spatial resolution that is similar 1e–15 2.0 T = 16 000 (K) to that of the HST (~ 0.07 arcseconds), eff but with spectroscopic information for 1.5 each single pixel (see Figure 1). A peak in 1.0 the centre of the cluster reveals how the 4800 4900 5000 5100 5200 5300 5400 5500 Wavelength (Å) spatial resolution is sufficient to resolve the WR stars R136a1, 2, and 3 (see the inset in Figure 1). star-forming region in the . stars in the vicinity of R136. However, the Its proximity makes it a perfect laboratory R136 cluster is impossible to resolve with in which to resolve the stellar population MUSE-WFM. R136 cluster: dissecting and modelling and test evolutionary theories. NGC 2070 hosts the most massive stars reported MUSE-NFM, commissioned in 2018 MUSE-NFM has unveiled a treasure-trove in the literature (Crowther et al., 2010), (Leibundgut et al., 2019), has opened a of OB stars to advance our understand- enclosing the massive cluster R136 at its window for optical stellar spectroscopy ing of the stellar evolution of very massive core. Understandably, NGC 2070 has been that until now was only available to the stars. Based on the integrated light of the of great interest to stellar astrophysicists, HST. The field of view of 7.5 × 7.5 arcsec- MUSE-NFM data cubes, we created a and it is considered the Rosetta Stone of onds and an expected spatial resolution new catalogue of the stellar content of the field (Schneider et al., 2018). However, close to that of the HST offer unique the cluster. The MUSE-NFM catalogue in light of the severe stellar crowding in capabilities for mapping R136. These lists approximately 1900 sources in ten the core of NGC 2070, the R136 cluster capabilities have been successfully tested fields, with a cutoff in theV band at has largely been omitted from many opti- during ESO programme 0104.D-0084. ~ 22 magnitudes. A first crossmatch with cal surveys (Evans et al., 2011). We observed ten fields in NGC 2070 with the Hubble Tarantula Treasury Project

The integral field spectrograph (IFS) MUSE (Bacon et al., 2014) on the VLT is capable of resolving crowded stellar Figure 3. Distribution of fields and taking high-quality spectra of 120 the representative OB thousands of stars in the dense cores of 4.0 stars (see Figure 2) in 60 the spectroscopic HR globular clusters (Kamann et al., 2016). diagram (Langer & In fact, this capability has even been 40 Kudritzki, 2014). The 32 positions of the O-type exploited out to nearby galaxies (Roth, )

๬ 3.5 and early B-type stars L

Weilbacher & Castro, 2019). The large / (blue dots) mainly match L 20 field of view and sensitivity of MUSE have the expected young age allowed us to systematically analyse large log( 15 of NGC 2070, approxi- stellar populations in unprecedented 3.0 mately 2 Myr (for exam- detail, and to study the ISM (for example, 12 ple, Schneider et al., 2018). Rotating evolu- Weilbacher et al., 2018; Roth et al., 2018). 9 tionary tracks from Castro et al. (2018a) presented MUSE log(Age [yr]) = 6.0 Ekström et al. (2012) 2.5 log(Age [yr]) = 6.5 wide-field-mode (MUSE-WFM) observa- 7 M are included in the plot log(Age [yr]) = 7.0 ๬ tions of the central part of NGC 2070. (dotted black lines). The isochrones were This work provided a homogeneous 4.84.7 4.64.5 4.44.3 4.24.1 calculated using the 1 spectroscopic census of the massive log(Teff [K]) SYCLIST online tool.

The Messenger 182 | 2021 51 Astronomical Science Castro N. et al., Mapping Stars in the Tarantula Nebula with MUSE-NFM

Figure 4. O+O spectroscopic binary resolved with 1.3 300 Field B MUSE-NFM. On the left, the kinematic evolution Field D 200 of He II 5411 Å (black line) at different epochs in ) x 1.2 –1 overlapping fields. We perform a preliminary charac- s flu

terisation of the binary using Gaussian models

m 100 (k 1.1 Field C (coloured lines). On the right, the velocity of each

65 0 component is displayed. Note that the blue compo- –2 nents of fields D and C overlap. The systemic veloc- d.

1.0 ra Normalised –1

v –100 Field B Field D ity of R136, 265 km s , has been subtracted. 0.9 –200 Field C He II 5411.61 Å –300 5400 5410 5420 5430 58 810 58 820 58 830 58 840 Wavelength (Å) Time (MJD) catalogue (HTTP; Sabbi et al., 2013) Stellar atmosphere characterisation is resolved spectroscopic binaries were showed additional detections and better indeed possible. As shown in Figure 3, detected in the extracted spectra. Figure 4 accuracy for some of the fainter sources the stars shown in Figure 2 match well shows an example of an O+O binary sys- close to the brightest stars that are satu- the expected young age of NGC 2070, tem, where both He II 5411 Å components rated in some of the HST images. The approximately 2.5 Myr. The full analysis are resolved. A Gaussian modelling of data will allow us to extract the spectra of the 200 stars with S/N > 50 will popu- both components shows a maximum of ~ 200 stars with good signal-to-noise late the diagram, creating the building peak-to-peak variability of ~ 500 km s–1. ratio (S/N), a sufficient number and distri- blocks of a better understanding of the Close binaries can indeed be character- bution to obtain a clear snapshot of the formation and evolution of R136. Only the ised at MUSE’s spectral resolution. evolution of OB stars at the age of R136, coolest star of these five departs from the to approximately 10 M☉ in the HR diagram. expected young age, beyond the theoret- ical main-sequence proposed by Ekström An ISM shaped by the most massive The MUSE-NFM wavelength range of et al. (2012) (see Castro et al., 2018b). stars 4700–9300 Å does not cover the classic transitions used for spectral classification MUSE-WFM provided new insights into and stellar atmosphere analysis (Castro Binary fraction and stellar evolution the ISM around the most massive, newly et al., 2018a). These canonical features born stars (Castro et al., 2018a). The gas are located at bluer wavelengths than the Binary stellar evolutionary models have intensity and kinematics were mapped, MUSE cutoff. Nevertheless, MUSE-NFM shown that drastic effects on each mem- showing a bimodal blueshifted and red- data offer alternative diagnostics. For ber result from their evolving together. shifted motion with respect to the R136 O-type and early B-type stars, several He Interactions, mass transfer and eventual systemic velocity, thereby sketching out I (4713, 4921, 5876, 6678 Å) and He II mergers shape each star’s path in the HR the ISM in unprecedented detail. A peak (5411, 6683 Å) transitions are included. diagram and the time it spends in differ- in the core revealed redshifted, possibly Hα and Hβ lines and the bluest part of ent regions (for example, Wang et al., infalling, material surrounding the strong- the hydrogen Paschen series are also vis- 2020). If 70% of OB stars were indeed est X-ray sources (see Figure 11 of Castro ible, offering additional constraints on the tied to a companion (Sana et al., 2012), et al., 2018a). However, the kinematics effective temperature and gravity. the evolution of massive stars in isolation in the inner part of the cluster could not would be rare. The spectral resolution of be explored at the spatial resolution of Previous work (for example, Crowther et MUSE, around 50 km s–1, may be consid- MUSE-WFM. al., 2017) shows that stellar analyses with ered a limitation before attempting a MUSE datasets are possible. Figure 2 study of the OB star binary fraction. But MUSE-NFM can pierce and dissect the displays the analysis of five representative we expect massive close-contact spec- ISM kinematics in the highly dense R136 OB stars extracted from one of the cen- troscopic binaries to have strong radial cluster, where MUSE-WFM capabilities tral fields in R136. The analysis was per- velocity variations over short timescales, could not probe. Figure 5 shows a formed by comparing the observed spec- that can be monitored even with MUSE’s coloured image of the central fields using tra with a grid of FASTWIND (Puls et al., moderate spectral resolution. some of the strongest emission lines 2005) synthetic models (see Castro et al., in the MUSE wavelength range: [S II] 2018b). The five examples in Figure 2 Our programme was designed to probe 6717 Å, Hα and [O III] 5007 Å. The strong show a good match for the key diagnostic the capabilities of MUSE-NFM in a single emission in Hα and the extended stellar lines marked in the plot, i.e., Hβ, He I 4921 epoch. Nevertheless, the observations wings of the WR population are clearly Å and He II 5411 Å. The residuals observed were spread out in time for technical visible in Figure 5, as is the effect of the in the [O III] 4959, 5007 Å nebular lines are reasons, so for some of the stars we radiation carving out the ISM at HST-like indicative of the difficulty of performing an obtained data from multiple epochs (see spatial resolution. We have discovered impeccable sky subtraction, despite the Figure 1). These overlapping regions are several new Hα emitters in this first emis- outstanding spatial resolution. priceless for carrying out a preliminary sion map, probably linked to Oe/Be stars test of OB stellar variability. Several and/or pre-main-sequence objects. The

52 The Messenger 182 | 2021 latter are expected in an ongoing star-­ forming region such as NGC 2070. New insight into the formation of massive stars and feedback between the ISM with strong stellar winds and the radiative Mk33Sb Mk42 R134 pressure of the most massive stars will be delivered by MUSE-NFM observations.

Mk39 Future prospects

We are aiming to get a complete snap- R136a shot of the stellar evolution of the cluster R136 and to explore the role of different parameters (for example, binarity) in that evolution. However, the image quality reached in Period 104 and the time allo- Mk34 cated over the forthcoming semesters lead us to dream of further possible out- comes. Exploring individual targets of interest in R136 can help us to address open questions, for instance about the physics driving stellar winds in O-type stars. The rich WR population in R136 will N Mk35 Mk37Wab be examined, paying special attention to their strong and extended stellar winds. The data will include the strongest X-rays Mk37 sources in the field (see Castro et al., 7.5 arcseconds 2018a), undoubtedly linked to the most E massive WRs: Mk34, R136abc and R140ab (Crowther et al., 2010). wavelength range so that detailed chemi- Figure 5. MUSE-NFM colour-composite mosaic of the We will explore proper motions in combi- cal composition analyses will be possible. nine fields in the core of NGC 2070 sampling narrow filters around the emission lines [S II] 6717 Å (red), Hα nation with HST data over a baseline of ESO’s Extremely Large Telescope (ELT) (green), and [O III] 5007 Å (blue). The WRs in the field almost ten since the first HST pro- and the next generation of instruments, are labelled (for example, Crowther et al., 2010). gram (PI: Lennon GO-12499, GO-13359). such as the High Angular Resolution Mapping the runaway population and its Monolithic Optical and Near-infrared possible links with the cluster will bring Integral field spectrograph (HARMONI) Crowther, P. A. et al. 2017, The Messenger, 170, 40 insights into the different mechanisms — and the multi-object spectrograph Dorigo Jones, J. et al. 2020, 903, 43 Ekström, S. et al. 2012, A&A, 537, A146 dynamical ejection and/or a binary super- MOSAIC, will allow us to leave the Local Evans, C. J. et al. 2011, A&A, 530, A108 scenario — that have been suggested Group and explore clusters similar to Kamann, S. et al. 2016, The Messenger, 164, 18 to remove the stars from the cluster (for R136 in other galaxies and in even Langer, N. 2012, ARA&A, 50, 107 example, Dorigo Jones et al., 2020). stronger starburst environments. Langer, N. & Kudritzki, R. P. 2014, A&A, 564, A52 Leibundgut, B. et al. 2019, The Messenger, 176, 16 Maeder, A. & Meynet, G. 2000, ARA&A, 38, 143 The MUSE-NFM observations have Richard, J. et al. 2019, arXiv:1906.01657 revealed a detailed spectroscopic picture Acknowledgements Roth, M. M. et al. 2018, A&A, 618, A3 of the massive stellar cluster R136. The Roth, M. M., Weilbacher, P. M. & Castro, N. 2019, This project has been funded by the Deutsche AN, 340, 989 combined MUSE IFS capabilities (i.e., Forschungsgemeinschaft (DFG) – CA 2551/1-1. Sabbi, E. et al. 2013, AJ, 146, 53 field of view, spatial resolution and spec- Norberto Castro and Genoveva Micheva gratefuly Sana, H. et al. 2012, Science, 337, 444 tral coverage) outperform the HST, the acknowledge funding from BMBF 05A17BA1, and Schneider, F. R. N. et al. 2018, Science, 361, 7032 only installation capable of resolving the Peter Weilbacher and Andreas Kelz from BMBF Simón-Díaz, S. et al. 2017, A&A, 597, A22 05A17BAA for the MUSE-NFM project. Puls, J. et al. 2005, A&A, 435, 669 stellar content of R136 at optical wave- Weilbacher, P. M. et al. 2018, A&A, 611, A95 lengths. This is an outstanding techno- Wang, C. et al. 2020, ApJL, 888, L12 logical achievement, emphasising the References growing role of IFS for stellar astrophys- Bacon, R. et al. 2014, The Messenger, 157, 13 Links ics, whose future is very promising. Blue- Castro, N. et al. 2018a, A&A, 614, A147 MUSE (Richard et al., 2019) for the VLT, Castro, N. et al. 2018b, ApJ, 868, 57 1 SYCLIST: https://www.unige.ch/sciences/astro/ will open the much desired blue Crowther, P. A. et al. 2010, MNRAS, 408, 731 evolution/en/database/syclist/

The Messenger 182 | 2021 53