arXiv:1708.02177v1 [astro-ph.SR] 7 Aug 2017 oigishtcr n eoigaWl-ae (WR) Wolf-Rayet ( a winds ex- strong becoming present star, stars and the WR of core star. mass hot initial its the of posing half wind than slow more This ISM. expels the into expand that winds dust-rich M iesasetrterdsprin rlmnu levari- ( slow blue dense, luminous exhibiting or phase supergiant able red the enter stars sive physi- ISM. the the governs of that structures feedback cal of repre- source They main motions. strong the proper sent winds, and stellar fluxes, by photon factors: (ISM) ionizing different medium of interstellar combination the a enrich and structure oa,vr asv tr ( stars massive very novae, iisof sities eprtrsa ihas high with as gas of temperatures region adiabatically-shocked an produces tion nebulae ring so-called nebulae. the WR or flux forming UV material, developed newly the the ionizes whilst shell, a RSG/LBV into ejected previously material the compress and up sweep ˙ fe vligo h ansqec tg,vr mas- very stage, sequence main the off evolving After hogotterlvs eoeepoiga super- as exploding before lives, their Throughout ubemdl ugs htti idwn interac- wind-wind this that suggest models Bubble cetdfrpbiaini p 2017 - ApJ in publication for Accepted ≈ 2 nttt eRdosrnmı srfıia NMCampus Astrof´ısica, UNAM Radioastronom´ıa y de Instituto 10 − aitos n hp fNC39 eedo h nta configuratio initial the on depend Keywords: 3199 NGC of shape and variations, Gaia eua aeilwt h tla id h oiatpam temperat plasma dominant The exhibits region wind. be s eastern to stellar the studies, estimated the optical at with from gas pr material derived ii) nebular arc abundances and optical nebular 18 WR the for from to reported wind close W stellar regions from the sp the i) wind by of analysis fast variations: and the star abundance the of reveals of south-east effect region powerful the in the brighter unveiling 3199, NGC from ag of range R1,peual uaa tr eas pia mgso h n the the present of We images star. optical the bo because of a star, south-west be runaway emission to a suggested presumably been has 18, WR 3199 NGC nebula (WR) Wolf-Rayet The n ..Toal J.A. 5 e M ≈ ⊙ 10 rtdt ees,w ocueta R1 sntarnwysa and star runaway a not is 18 WR that conclude we release, data first 4 nttt eAto´sc eAdlcı,IACI,Glorie Andaluc´ıa, Astrof´ısica IAA-CSIC, de de Instituto − yr 5 1. eateto srnm,Uiest fIlni,10 West 1002 Illinois, of University Astronomy, of Department L 2 − ( a ´ X -as niiul(R18) (WR individual X-rays: S:bbls—sas ofRyt—Xry:IM—Xry:individua X-rays: — ISM X-rays: — Wolf-Rayet stars: — bubbles ISM: cm 1 1 INTRODUCTION =2.6 e.g., ; nttt fAtooyadAtohsc,Aaei iia( Sinica Academia Astrophysics, and Astronomy of Institute 杜 3 − uoenSaeAec/Tc,30 a atnDie Baltim Drive, Martin San 3700 Agency/STScI, Space European 宇 3 T T × 君 htfil h eua hl in- shell nebular the fills that =10 ≈ 10 ) M 1 1 34 aane l 2006 al. et Hamann O A NTEWL-AE EUANC3199 NGC NEBULA WOLF-RAYET THE IN GAS HOT , . 7 i 2 2 –10 ..Marston A.P. , × & r s erg 10 ∼ 8 0M 30 010k s km 10–100 6 n lcrnden- electron and K v − and K ∞ 1 obndwt nomto eie from derived information with Combined . ≈ ⊙ oiythe modify ) 50k s km 1500 n e 03cm =0.3 3 − ..Guerrero M.A. , 1 that ) ,and ), ABSTRACT − 1 − , 3 oei,Aatd otl37,Mrla500 Michoac´an, 58090, Morelia 3-72, postal Apartado Morelia, XMM-Newton iha -a uioiyi h .–. e energy keV 0.3–3.0 the in luminosity X-ray an with eir( terior as odcini ae noacut(e.g., account hydro- into of thermal taken if formation is augmented be conduction the can on and instabilities depend dynamical stongly region ing tde beto hscas hs uhr eotd for reported, authors These class. this of object studied by presented of material. those nebular to the close abundances exhibits gas X-ray-emitting 2011 warm the and bubble hot re- the the are between ( emission mixing X-ray of diffuse sult soft the by indicated 2012 al. 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Figure 1. Top left panel: Color-composite nebular image of NGC 3199. The colors red, green, and blue correspond to [S ii], Hα, and [O iii] line emission, respectively. Other panels show the [O iii]/Hα (top-right), [O iii]/[S ii] (bottom- left), and Hα/[S ii] (bottom-right) ratio maps. The position of WR 18 is shown with a red circle in all panels and the orientation of the figures is shown on each panel. The blue and magenta arrows show the direction of the proper motions reported by Hipparcos and Gaia observations, respectively (see text). The narrow-band images are courtesy of Don Goldman. Hot gas in the WR nebula NGC3199 3
−1 the first time in the X-ray regime, nitrogen and temper- to a projected velocity of v⋆ ≈ 55±20 km s along the ature variations within the WR nebula leading them to north-west direction. the conclusion that the mixing of material is not equally The present paper is organized as follows. The descrip- efficient in all directions. Apparently, the mixing has tion of our XMM-Newton observations and the analysis been less efficient towards the caps of NGC 6888, which are presented in Section 2. Our results are presented and presents higher temperature and nitrogen abundance, discussed in Sections 3 and 4, respectively. We finally while in the central regions the X-ray-emitting material summarize our findings in Section 5. has similar abundances as those reported for the nebu- 2. OBSERVATIONS AND DATA PREPARATION lar material (see Reyes-P´erez et al. 2015, and references therein). The WR nebula NGC 3199 around WR 18 was ob- On the other hand, there are two other WR neb- served by the European Science Agency (ESA) X-ray ulae that have not been detected in X-rays. These telescope XMM-Newton on 2014 December 1 in revolu- are RCW58 around WR40 and that around WR16 tion 2743 (Observation ID: 0744460101; PI: J.A. Toal´a). (Gosset et al. 2005; Toal´a& Guerrero 2013). These neb- The European Photon Imaging Camera (EPIC) was used ulae harbor WN8h stars with relatively slow stellar winds in the Extended Full Frame Mode with the Medium Opti- −1 (v∞ ≈ 650 km s ), while those that have been de- cal Filter. The total time of the observation was 56.8 ks tected in X-rays (S308, NGC2359, and NGC6888) have with exposure times of 51.4, 53.4, and 53.2 ks for the −1 WN4-6 stars with faster winds (v∞ ≈ 1700 km s ; EPIC-pn, EPIC-MOS1, and EPIC-MOS2, respectively. Hamann et al. 2006). Even though this wind velocity We processed the EPIC observations using the XMM- seems to be the only characteristic in common for dis- Newton Science Analysis Software (SAS) Version 15.0 playing diffuse X-ray emission, it can not be taken with with the corresponding Calibration Access Layer ob- certainty as the current number of studied WR nebulae tained on 2016 February 26. The event files have been in the X-ray regime is small and the global properties of produced from the Observation Data Files by using the the X-ray-emitting gas may depend on other stellar and tasks epproc and empproc included in SAS. We identified nebular properties, including the stellar evolution, for- periods of high-background level by creating light curves mation mechanism, ISM structures around the nebulae in the 10–12 keV energy range with a binning of 100 s (see discussion by Toal´aet al. 2016). for each of the EPIC cameras. We rejected times with −1 In this paper, we present XMM-Newton observations count rates higher than 0.3 counts s for the EPIC-pn −1 towards NGC 3199 (see Fig. 1) around the WN4 star camera and 0.2 counts s for the MOS cameras. The WR 18 (Teff = 112.2 kK; Hamann et al. 2006). Archival resulting useful exposure times for the pn, MOS1, and ROSAT observations (Obs. ID. RP900318N00) hinted at MOS2 cameras are 36.1, 48.9, and 49.1 ks, respectively. the presence of diffuse X-ray emission, but the X-ray 2.1. Spatial distribution of X-rays in NGC 3199 point sources projected within the nebula, including that of WR 18 (e.g., Skinner et al. 2010), prohibited an un- To study the spatial distribution of the X-ray-emitting ambiguos analysis. Unlike other WR nebulae detected gas in NGC 3199, we have used the XMM-Newton Ex- in X-rays, this nebula has been the center of discussions tended Source Analysis Software package (XMM-ESAS) as some authors suggest that the abundances are close included in the current SAS version. We have followed to galactic H ii regions (see, e.g., Whitehead et al. 1988; the ESAS cookbook for the analysis of extended sources 2 Stock et al. 2011), while others suggest that some regions version 5.9 to create maps of the extended X-ray emis- within the nebula exhibit significant chemical enrichment sion in NGC 3199 and to identify potential contaminant (e.g., Esteban et al. 1992; Marston 2001). point sources. Figure 1 shows in great detail the optical morphology We have created EPIC images in the energy bands and extension of NGC3199. The nebula has an elon- 0.3–1.1, 1.1–2.5, and 2.5–5.0 keV that we label as soft, gated shape with angular size of ∼20′×25′ as mapped medium, and hard X-ray bands, respectively. Individual by the [O iii] narrow-band emission but with an obvi- pn, MOS1, and MOS2 images were extracted, merged ous enhanced emission towards the west, the bright arc together, and corrected for exposure maps. Figure 2 (see also Whitehead et al. 1988). This arc was the defin- shows the resultant background-subtracted EPIC image ing factor for Dyson & Ghanbari (1989) to suggest that of the soft band and a color-composite picture of the NGC3199 is composed of swept up ISM material in a bow three X-ray bands. Each X-ray image has been adap- shock around WR18, which is not located at the geomet- tively smoothed using the XMM-ESAS task adapt re- rical center of the nebula. In fact, Hipparcos reported quiring 80, 80, and 30 counts for the smoothing kernel for the soft, medium, and hard band, respectively. a proper motion for WR18 of (µα, µδ)=(−2.30±1.75, −1 4.78±1.35 mas yr ) (Perryman et al. 1997), which at a 2 http://heasarc.gsfc.nasa.gov/docs/xmm/esas/cookbook/xmm- distance of 2.2 kpc (see van der Hucht 2001) corresponds esas.html 4
0.3 - 1.1 keV 0.3 - 1.1 keV 1.1 - 2.5 keV 2.5 - 5.0 keV -57:40:00.0 -57:40:00.0 Background 45:00.0 East 45:00.0 West 50:00.0 50:00.0 WR 18 WR 18 55:00.0 55:00.0 Dec. (J2000) Dec. (J2000) -58:00:00.0 -58:00:00.0 05:00.0 05:00.0
30.0 19:00.0 30.0 10:18:00.0 30.0 17:00.0 30.0 16:00.0 30.0 19:00.0 30.0 10:18:00.0 30.0 17:00.0 30.0 16:00.0 R.A. (J2000) R.A. (J2000)
Figure 2. XMM-Newton EPIC (MOS1+MOS2+pn) exposure-corrected images of the X-ray emission from NGC 3199. Left: Soft band (0.3–1.1 keV). Right: Color-composite X-ray image. The colors red, green, and blue correspond to the soft, medium, and hard X-ray bands, respectively. The central star, WR 18, is shown with a circular aperture in both panels. The regions used for source spectral extraction are shown by solid lines whilst the background region by dashed line. No point sources have been excised from these images.
Figure 2 shows the presence of diffuse X-ray emission tively) presented in Fig. 1 with the resultant soft X-ray within the WR nebula NGC 3199, as well as a large num- image (blue). It can be seen that the diffuse X-ray emis- ber of point-like sources projected on the nebula. The sion in NGC 3199 is delimited by the [O iii] as in other central star, WR 18 is detected confirming the previous WR nebulae, filling the cavities observed in narrow-band Chandra detection Skinner et al. (2010). It seems that nebular line images. Moreover, the extended X-ray emis- the most intense X-ray emission region is located to- sion is considerably brighter toward the east. ward the east of the nebula, in particular, the south- east region. Furthermore, the X-ray colors unveil spec- 2.2. Spectral extraction tral differences within the diffuse X-ray emission: the To study the physical properties of the X-ray-emitting eastern regions emit predominantly soft emission (0.3– gas in NGC3199, we have extracted different spectra: i) 1.1 keV) while the western region emits significantly in a spectrum that includes the extension of the main cavity the medium X-ray band (1.1–2.5 keV). To further il- as seen by the [O iii] narrow-band emission, in order to dmfilth lustrate this, we have used the CIAO routine estimate global properties of the diffuse X-ray emission, (version 4.8, Fruscione et al. 2006) to cut out all de- ii) spectra from smaller apertures to study variations in tected point-like sources and create a direct compari- physical properties of the hot gas in the nebula, and iii) son between the nebular emission and the distribution of a spectrum of the central star WR18. Three different the X-ray-emitting gas. The identification of the point polygonal apertures have been defined as shown in Fig. 2. sources has been performed following the EPIC source 3 We label the different spectra as NGC3199, West, East, finding thread . This allowed us to perform a search for and WR 18. point sources in different energy bands (0.3–0.5 keV, 0.5– All identified point-like sources have been removed 1.0 keV, 1.0–2.0 keV, 2.0–4.5 keV, and 4.5–12.0 keV) for prior to the spectral extraction. We only used the EPIC- the three EPIC cameras. pn spectra of the diffuse X-ray emission given the supe- Figure 3 shows the comparison of the nebular [S ii] rior quality as compared to the EPIC-MOS spectra. In and [O iii] narrow-band images (in red and green, respec- the case of the central star, however, the smal numbers of 3 See http://www.cosmos.esa.int/web/xmm-newton/sas-thread- counts forced us to use the three EPIC spectra for a bet- src-find-stepbystep ter determination of the physical parameters (see below). Hot gas in the WR nebula NGC3199 5
Figure 3. Color-composite image of NGC3199 around WR18. Red, green, and blue correspond to [S ii], [O iii], and the soft X-ray band (0.3–1.1 keV), respectively. All point-like sources have been cut out from the X-ray image except WR 18 (see text for details). The position of WR 18 is shown with a red circle whilst other circles mark the positions of the nerby Tycho-Gaia Astrometric Solution stars in the field of view. The black circle shows the position of the BOV star CD−57◦3120 (see Discussion). North is up, east to the left.
Figure 4 presents all background-subtracted spectra. do not adequately model the local Galactic background. WR nebulae are mainly located in the Galactic Plane, While useful for the extraction of spectra of extragalactic where the large absorption column density and signif- objects, the Blank Sky observations can not be used for icant background emission (e.g., Snowden et al. 1997) objects placed in the Galactic Plane (see also figure 3 and pose significant difficulties for the study of their ex- section 4.1 in Toal´aet al. 2014). Therefore, the back- tended X-ray emission. The spectrum of the back- ground spectrum extracted from the region surrounding ground extracted from the region near the camera edges NGC3199 has been used. outside of NGC3199, as defined in Fig. 2-left, has a significant contribution in the 0.3–3.0 keV energy 3. RESULTS range (Figure 5), where the diffuse X-ray emission from All spectra have been modelled using XSPEC NGC 3199 mainly concentrates. Toal´aet al. (2012) dis- v.12.9.0 (Arnaud 1996) with a two-temperature vapec cussed the possibility of using EPIC Blank Sky obser- plasma emission model using a tbabs absorption model vations (Carter & Read 2007) for the case of S308. By (Wilms et al. 2000). The resultant model spectra were definition, these blank fields have flat spectra, but they compared with the observed spectra in the 0.3–3.0 keV 6
NGC 3199 WR 18 0 0 0