arXiv:2005.10368v1 [astro-ph.GA] 20 May 2020 at o xml,Mjese l 20)loe o ikbe- 1315 link PHR p PN a in of led for discovery which the cluster, looked open to (2007) an (PNe) al. nebulae et planetary Majaess tween in example, researchers helped For have catalogues past. the Numerous which astrophysics. in in works tool the important an are Catalogues Introduction 1. aaoswr h trigpit o oeipratdeterm important T some masses. for points tions. their starting e determined the with were literature, catalogs together the and, from locate PNe magnitudes they the the parallaxes providing of these thus Using CS objects. parallaxes, 430 Gaia to DR2 parallax with canonical PNe matched post-common-envelope of (2020) trometry al. only et tha Stanghellini fact the recently, More the bipolar. being changing post-common Thus 2346 2009b), of nebulae. al. 60% NGC bipolar et least (Miszalski are at work of PNe of fraction envelope up a sample follow that independent a concluded a in they in and, 10-20% PNe was binary tha fraction established binary OGLE also and close They 2014). PNe catalogues. at al. cross-matching survey et binaries by (Majaess microlensing nebulae periodic planetary solution 21 of discovered distance center (2009a) 4% al. a et Miszalski and 1 Lindsay a 2 2020 22, May Astronomy n log and e words. Key H- that shown database. is Vizier it the Moreover, through nebulae. available planetary form to able hrfr etnn nomto smrl vial for stell available of merely stage is late information potential pertinent a therefore represent nebulae Planetary 2020 22, May h odtosrqie o h omto fHpo SN Ap CSPN. H-poor of formation the evolutionar for that required suggests finding conditions last the The group. H-rich the eeecsfrpbihdseta h akdsaitcli statistical marked H-rich The the spectra. published s parameter for physical important references includes featuring and 25%, CSPNe by 620 iteration of existing catalogue new a construct 1 2 6 5 4 3 edan .A. W. Weidmann, bevtroAtoóiod ódb.UiesddNaciona e-mail: Universidad Córdoba. de Astronómico Observatorio osj eIvsiainsCetfia éncsd aRepú la de Técnicas y Científicas Investigaciones de Consejo autdd inisAtoóia efscs NP Buen UNLP, Argentina Geofísicas, Aires, y Buenos Astronómicas Ciencias de Buenos Facultad CONICET–UNLP, Plata, Argentina La Aires, Buenos de Astrofísica de Instituto bevtrod aog,Uiesdd eea oRod Jan de Rio do Federal Universidade Valongo, do Observatório nttt eAtooí erc xeietl CONICET–U Experimental. y Teórica Astronomía de Instituto & g xii assadae ossetwt igeselrevo stellar single with consistent ages and masses exhibit , [email protected] / Astrophysics -orrtoi :,teei ecec fCPewt ye [ types with CSPNe of deficiency a is there 2:1, is ratio H-poor aaos–paeaynble eea tr:evolution stars: – general nebulae: planetary – catalogs aaou fcnrlsaso lntr nebulae planetary of stars central of Catalogue 1 , 2 ai .B. M. Mari, , aucitn.aanda no. manuscript uire-oo .A. L. Gutiérrez-Soto, − 55i h lse Andrews- cluster the in 6555 ff cietmeaue and temperatures ective 4 cmd,E O. E. Schmidt, , xaddedition Expanded 4 op .G. M. Volpe < poeetealdtefloigprietcnlsosto conclusions pertinent following the enabled mprovement h as- the 0 fteGlci ape osqety h ieauewa literature the Consequently, sample. Galactic the of 20% uha uioiy ufc rvt,tmeaue magnit temperature, gravity, surface luminosity, as such s reouin oee h eta tr CPe r relativ are (CSPNe) stars central the however evolution, ar the d cnro edn otefraino iaycnrlstars central binary of formation the to leading scenarios y the t ABSTRACT ina- the are the art orCPeaefre yhge aspoeios h catalo The progenitors. mass higher by formed are CSPNe poor he 3 rxmtl 0 ftesml ihdrvdvle flog of values derived with sample the of 50% proximately eta lsictosadifrain h aaou sup catalogue The information. and classifications pectral apr G. Gaspar, , eCroa ard 5,Croa Argentina Córdoba, 854, Laprida Córdoba. de l lc retn,Argentina Argentina, blica - t io aer er noi 3 08-9 i eJnio Br Janeiro, de Rio 20080-090 43, Antonio Pedro Ladeira eiro, C ódb.Lpia84 ódb,Argentina. Córdoba, 854, Laprida Córdoba. NC, sArs retn ae e oqes Bosque del Paseo Argentina Aires, os rgntrsa hc ol euti Ni rqetyes- frequently is the PN of a masses in of result range would pr the which the Although star as PNe. progenitor such of models, mass evolutionary genitor’s to limits observational 2014). 2. happ SuWt Mugrauer might and & common, 5 (Adam be LoTr to in 246 speculated is nucl NGC which the situation, nebula at This system planetary triple of the a Also multiplicity identify [WR] of the to 2010). the possible to al. of was regard et it With is (Todt CSPNe, 2015). star 8 al. primary al. et whose PB (Manick et system (Miszalski type at binary 4663 probably a 5189, IC and NGC i.e. several 48, Moreover, confirmed, A for be 2015). apply, 2012b), longer could al. et no stars (Weidmann that [WN] wels types the spectral are example concerning There th published CSPNe. been during the have addition, developments In new necessary. many years becomes catalogue that of ieyasteehsbe nices ntenme fCSPNe of bet last is through number improved the useful the (or in quality information during types a increase spectral as determined an be new been limited But with has to community. there proven with astronomical years nine has the but for It tool (2011b). catalogue Gamen & Weidmann complete a ie,AgniaPsodlBsu s Bosque del Paseo Argentina Aires, uinr oes h mlcto sta igesasaei are stars single that is implication The models. lutionary 3 ae,R. Gamen, , aaou ol lo ttsia nlssadprovide and analysis statistical allow would catalogue A eadn h eta tro lntr eua (CSPNe), nebulae planetary of star central the Regarding C56,adnal 0 fbnr eta tr eogto belong stars central binary of 80% nearly and 5-6], WC / eouinsetaa edane l 08,a upgrade an 2018), al. et Weidmann as spectra resolution 1 , 2 ilrBroai .M. M. Bertolami, Miller , 5 , 6 at D. Mast, , 1 , 2 / / ,FA 10 aPlata, La B1900 FWA, n, ,FA 10 aPlata, La B1900 FWA, n, ril ubr ae1o 46 of 1 page number, Article 5 , 6 d siae,and estimates, ude i,G A. G. Oio, , edetermined: be nefr with interfere uvydto surveyed s l an and faint ely ree the ersedes L log ,
c azil S 2020 ESO u is gue ndeed T 3 e ff , , eus ese the ter en o- A&A proofs: manuscript no. aanda timated to be between 1-8 M⊙, the observational evidence in and Napiwotzki (1998) present a collection of spectra of differ- support of this point is limited. Nevertheless, the confirmation ent spectral types of evolved objects which represents a useful of a PN associated to an open cluster, has a direct implica- tool. In Table 1 we mention some key lines of each spectral type. tion on the upper limit on the progenitor’s mass. Fragkou et al. Nevertheless, these do not replace the proper classification crite- (2019a) and Fragkou et al. (2019b) have proved that the PNe ria of every type. Below we present a guide, with bibliographic PHR 1315−6555 and BMP J1613−5406 are physically linked references, that describes the spectrum (in the optical range) of to an open cluster. Consequently we have, for the first time, each type of object mentioned in our catalogue. observational evidence that the upper limit of the initial stellar mass for the formation of a PN can be as high as M∗.5.0 M⊙. – [WR] (subtype [WN], [WC] and [WO]): Crowtheret al. Another important step forward in the study of the formation (1998), Acker & Neiner (2003) and Miszalski et al. (2012b). of PNe came from the study of Hen 2−428, whose central star The spectral type VL was implemented by Górnyet al. was found by Santander-García et al. (2015) to be composed of (2009), which is in fact consistent with a late [WC]. a double-degeneratecore with a combined mass above the Chan- – O(H): Although these objects follow the classification crite- drasekhar limit. Although later studies have put such high mass ria for massive O-type stars, in Weidmann et al. (2018) some into question, favouring a much lower mass for the central stars characteristics of the O-type stars that are CSPNe are de- (e.g. García-Berro et al. 2016; Reindl et al. 2018). Specifically, scribed. In this type of stars it is possible to improve the the detailed analysis of Reindl et al. (2020) indicates that the spectral classification with qualifiers (Sota et al. 2011, 2014; system might be composed of a 0.66 M⊙ post-AGB and a re- Maíz Apellániz et al. 2016). Based on the ions identified in heated 0.42 M⊙ post-RGB star. The study of this peculiar object the spectrum, the CSPNe could be classified as O(H), O or will certainly shed light on the formation process of PNe through H-rich (Weidmann et al. 2018). common envelope events. – Of(H): This includes the O-type stars with emission lines. To establish an evolutionary sequence involving the spectral Historically, there was a distinction between the O-type and types of the CSPNe was not a simple task, and certainly, we still Of-type stars. Nevertheless, not all O-type star with emission have a lot to learn about this topic. Proof of this is the case of lines are in fact an Of-type. To clarify this see Mendez et al. Hen 3−1357.Reindl et al. (2017) observed that the CSPN of this (1990); Smith & Aller (1969). In Sota et al. (2011) these ob- object is evolving quickly, changing from B-type (T ∼ 21 kK) jects are indicated with the qualifiers: f, f*, fc and f+. eff – O(C): This type of star appears only in one member, i.e. object in 1971 to a Teff ∼ 60 kK peak in 2002. Since then it seems to be cooling and expanding back to the AGB at a rate K3−67. Previously, Lo 4, wray 17−1, and IsWe 1 were in- of 770 ± 580 K yr−1, similar to that of FG Sge (350 K yr−1 cluded in this spectral type (Mendez 1991). Nowadays, these Jeffery & Schönberner 2006) and providing further evidence of last three objects were reclassified as PG 1159. the existence of late helium flashes in the post-AGB evolution. – O(He): Reindletal. (2014b), Rauchetal. (2008), Rauch et al. (2006) and Rauch et al. (1998). In summary, in the last years a series of extreme phenom- – Of−WR(H): Mendez et al. (1990) and Mendez (1991). ena has been found in PNe that increase the complexity of these – WD (subtype DA, DAO and DO): Napiwotzki (1999), objects. Undoubtedly, the less understood stage of stellar evolu- McCook & Sion (1987), and McCook & Sion (1999). tion for low and intermediate mass stars is precisely the last one, – hgO(H): The classification hgO(H) was used exclusively for i.e. from post-AGB to pre-WD. This is the main motivation to CSPNe (Mendez et al. 1986), these objects are essentially update and expand the catalogue of CSPNe. Thus, in this work evolved objects like sdO or WD stars. For example Sh 2−68 we present a new catalogue of spectral types of CSPNe which have three classifications i.e. hgO(H), WD, and PG 1159 supersedes the Weidmann & Gamen (2011b). (Napiwotzki & Schoenberner 1995). This paper is structured as follows: In Section 2 we present a – sdO, sdB: Jeffery et al. (1997) and Ahumada et al. (2019). summary of the different spectral types of CSPNe. An evolution- – PG 1159 (subtype A, E and lg E): Werner (1992), ary sequence is described in Section 3. We detail the main body Dreizler & Heber (1998) and Hügelmeyer et al. (2005). of the catalogue in Section 4. Results are presented in Section 5, – [WC]−PG 1159: Previously called Of-WR(C) (Mendez while in Section 6 there is a summary of this work and we lay 1991). There are only two objects with this spectral type, our conclusions. Finally, in the Appendix we focus on peculiar A 30andA 78. CSPNe. – hybrid: Dreizler et al. (1996) and Napiwotzki (1999). – symbiotic star (SySt): This is not strictly a spectral type (see Appendix A). 2. Review of spectral classification – B[e]: Oudmaijer&Miroshnichenko (2017) and Lamers et al. (1998). It is well known that the CSPNe are divided into two large – cont.: Weidmann et al. (2018). This is not strictly a spec- groups. Those that present hydrogen absorption lines (H-rich) tral type. In general, objects with this designation are O-type and those that do not (H-poor). One of the pioneering work in stars. compiling CSPNe spectral information was Aller (1975). He re- – B2-M9: Objects later that a B1 does not have the required ported the following types: O-type, WC, OVI (currently called temperature to ionize the nebula. In this sense, objects clas- [WO]), Of + WR, sdO and continuum. sified with a late type are, in fact, candidates for binary sys- There are few spectral types that are specific of CSPNe i.e. tems whose hot component is hitherto undiscovered. O(C), [WC]-PG 1159, and Of-WR(H). For the [WR], O and Of- – wels: Classification implemented by Tylenda et al. (1993). type, the classification criteria for massive WC stars (or massive This designation has been shown not to correspond to an in- O-type stars) is used. Implementing an appropriate criteria for dependent spectral type. In general it contemplateshot O(H)- CSPNe requires a large number of good quality spectra. type stars (Weidmann et al. 2015). It is appropriate to point out that this is a qualitative classi- – EL (Emission Line): Few objects in which the presence of fication system in which the unknown stellar spectrum is com- emission lines of stellar origin have been reported. These ob- pared with a grid of standard stars. In this sense, Dreizler (1999) jects do not always satisfy the wels criterion.
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– Blue: The MASH catalogue identified CSPNe of some ob- jects. Photometric observations indicate that these objects are blue. None of these objects have spectroscopic information.
3. Review of stellar evolution The main parameter that defines the stellar evolution is the mass. It is commonly accepted that the mass range of a main sequence star that gives birth to a PN is 1.0 M⊙ . M∗ . 8.0 M⊙. However, this mass range is not a strict limit. Firstly, the minimum mass required to form a star is 0.07 M⊙, the hydrogen burning mass limit (Chabrier & Baraffe 2000). Therefore, stars with mass in the range between 0.07 M⊙.M∗.1.0 M⊙ do not evolve to a PN. In fact, these stars did not have enough time to leave the main sequence (Miller Bertolami 2019). Saracino et al. (2016) estimated the globular cluster turn-off mass in about 0.88 M⊙ for NGC 6624. In this sense, it should not have progenitor CSPN with masses lower than 0.88 M⊙. A PN is obtained when the gas expelled in the AGB phase is ionized by the remaining object at its core. This requires a star with a certain minimum progenitor mass Mχ. Objects with mass less than Mχ will not result in a nebula. Observational data must be used to obtain Mχ. Globular clusters are the oldest objects Fig. 1. An evolutionary sequence model, the classical picture. in the galaxy and the lifetime of a PN is about 20000 years. Hence, if it is possible to determine the progenitor mass of a PN that is physically linked to a globular cluster, this will be The evolutionary state of B[e] CSPNe is unknown too. The a good estimation for Mχ. Jacoby et al. (2017) showed that the nebulae that contain these stars are compact and with high- progenitor mass of the PN JaFu 1 (planetary nebulae linked to density. These nebulae are often classified as protoplanetaryneb- the globular cluster Pal 6) is 0.8 M⊙. ulae (PPNe) or young PNe (Clegg et al. 1989). These objects On the other hand, finding observational evidence for the up- have stellar hydrogen emissions and are therefore considered per limit on the stellar mass, required to originate a PN, is not to belong to the H-rich group. The O(He) stars are even more so straightforward. An option is to determine the mass of the complicated,(see, e.g., Reindl et al. 2014b; Rauch et al. 1998) as progenitor star of a PN linked to an open cluster. Fragkou et al. they are speculated to have multiple possible evolutionary paths. (2019b) showed that the progenitor mass of the planetary nebula One possible evolutionary path is Merger(CO WD + He WD)→ BMP J1613−5406 (object linked to the open cluster NGC 6067) RCrB → EHe → O(He) → DO (Reindl et al. 2014b). It is neces- is5M⊙. sary to identify more objects of this type in order to clarify this Now, how is the evolutionary sequence for a main sequence point. star with mass between 0.8 − 5.0 M⊙? Which is the spectral- The same situation happens with the [WN] type. There are type sequence it passes through? These questions still have no only three well-known objects, with an unclear evolutionary single answer. Iben (1991) developed a convincing theoreti- state. One possibility is that [WN] → O(He) (Todt et al. 2017). cal model, but it does not contemplate the spectral types. Per- The hybrid objects (or hybrid PG 1159-type) are strange ob- haps the sequence shown in Fig. 1 is the most classical pic- jects (Löbling et al. 2019). This type include four objects, being ture (see, e.g., Leuenhagen & Hamann 1998; Zijlstra et al. 1994; one of them not in the core of a PN. Dreizler et al. (1996) sug- Peña et al. 2001; Koesterke 2001; Werner & Herwig 2006). In gest two possibilities: [WC 12] → hybrid → PG 1159 or [WC addition, a more complex and complete (includingseveral specu- 12] → hybrid → DAO. lations) evolutionary path is presented by Danehkar (2014). The Finally, the Of−WR(H) CSPNe belong to the H-rich group. stellar post-AGB evolution divides into two major channels ofH- There are not references regarding its evolutionary status. They rich and H-poor stars (Löbling et al. 2019). However, other evo- may be binary objects. lutionary pathways exist (see, e.g. Fig. 14 of Frew et al. 2014). Nevertheless, it is necessary to clarify that these sequences are 4. The catalogue of CSPNe valid only for a single star. The CSPNe with spectral type sdO, B[e], O(He), [WN], hy- This new version of the catalogue contains 620 galactic objects, brid and Of−WR(H) are not included in this classical evolution- representing an increase of 25% compared to the previous ver- ary picture. sion. However, it is not only in the number of objects that the The origin of the sdO is yet not clear. Probably, this ob- real impact of the new version lies. We also report many spec- ject comes from low mass progenitors (Reindl et al. 2014a), and tral type changes. For example, the core of He 2−47 that was couldend up as a WD (Aller et al. 2013). Aller et al. (2015a) ob- previously classified as a [WC], has now been catalogued as an served that the sample of PNe with a sdO nucleus are faint and O(H)-type star based on newer, better quality spectra. Besides, can be found at relatively high Galactic latitudes, which would new high-qualityspectra made possible to improveand refine the suggest they are in a moderate or evolved stage and evolving previous classification, as is the case of Sa 1−8 (from OB type from low-mass progenitors. In the work of Heber (2009), sev- to O(H)4−8 III). In addition, some objects were rejected in the eral evolutionary paths are considered. new version because we currently know that they are not PNe.
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Table 1. Key optical lines to spectral classification of CSPNe. Upper panel represents narrow features, and lower, wide features. The ions are arranged by excitation potential. In the second column we propose a prototype with published spectrum.
ion/wavelength [Å] Spectral Example H i He i C iii C iii He ii He ii C iv C iv N v N v O vi O vi classif. 4340 4471 4649 5696 4686 5412 5806 4650 4603 4945 3822 5290 earlyO(H) NGC5307 A A - - A A E - A - E? E lateO(H) Cn3−1AAA-AAA----- earlyOf(H) M1−53AAE - EAE -A- ?E lateOf(H) IC4593 A A A - E A ? - - - - ? Of-WR(H) NGC6543 A ? - - E1 EE-E- -E O(He) He2−64- - - -AA- -EE- - PG1159 Jn1 - - - - A A E A - - E E [WO] NGC2867 - - - - E E E E - - E E [WC] NGC40 - - E E E E E - - - - - [WN] IC4663 - - - - E E - - E E - E DA DeHt5 A ------DAO HDW3 A - - - A ------DO KPD2 -A--AA------
Notes. 1 Wide line. 2 KPD 0005+5106
This is the case, for example, of Sh 2−128 (Bohigas & Tapia unless there is a large discrepancy. In that case, we include 2003). Moreover, in this new version, we include physical pa- both classifications. All of them are described in Section 2. rameters such as temperature, luminosity, and surface gravity, We maintain the notation given by different authors, in this which were obtained from the available literature. On the other context we keep the classification wels. Nevertheless, the hand, we added the apparent magnitude (a key parameter for spectrum can change in a short period of time. Bond (2014) planning an observation), and a bibliography reference where showed that the CSPN of Lo 4 had a short-time mass loss the stellar spectrum is shown. This allows future researchers to episode, manifested by the appearanceof new emission lines. re-evaluate the spectral classification or to obtain a better qual- – c10: Reference of multiplicity, taken from the actual web of ity spectrum. In this sense, it is important to note that there are Dr. David Jones1. We do not included binaries detected by J few spectra available in the literature, in particular of [WR]- or I-band excess. type. Also, in general, the spectral classification of these objects – c11: Reference of the optical spectra. has not been confronted with new observations. Crowther et al. (1998) and Acker & Neiner (2003) are perhaps the two most im- 4.2. Table 2: physical parameters portant works dealing with spectral classification of [WR]. Both works include important object samples however the published – c1: PN G designation. The first nine objects do not have spectra do not allow to properly check the spectral classifica- PN G, then we use the recno number of Table 1. tion. The catalogue is divided into two tables. The former with – c2-3: Surface gravity (log g, cm s−2) and reference. t.w. the spectral type and the second one with physical parameters. means this work. We computed log g according to equa- In the following sections, we describe each column of the two tion 17 of Zhang&Kwok (1993) with data take from main tables. Gesicki & Zijlstra (2007). – c4: The method by which the temperature was determined. We prefer the effective temperature (Te f f ). Nevertheless, in 4.1. Table 1: spectral types the catalogue we include other temperatures, Zanstra temper- – c1: The PN G designation, taken from SECGPN. atures TZ(He I)orTZ(He II) (Phillips 2003) or the photoion- – c2: The flag indicates that the object could not be a PN. ization (equivalent black-body) temperature (Gesicki et al. – c3: The common name of the object, taken from SECGPN 2006). Hoare et al. (1995) show the different results obtained and MASH. for CSPN temperature using different methods. – c4-5: The equatorial coordinates (J2000.0). Frequently, it is – c5-6: Temperature and reference. In the case of the H-rich not clear which is the CSPN either because the star is not at group, it is possible to estimate the temperature inspecting the geometriccenter of the nebula, due to the interactionwith the spectra and looking for He i absorption lines. The absence the ISM or because of the object lies in crowded star fields. of these lines indicates that the central star is hotter than 70 For example the PN Sh 2−71 (Mocnikˇ et al.2015)orK4−37 k (Kepler et al. 2016). (Miranda et al. 2017). The problem worsens when the PN – c7-8: Bolometric luminosity (log(L⋆/L⊙)) and reference has a large angular size, which may lead to incorrect identi- (e.g. Zhang & Kwok 1993). fication of the CSPN (e.g. Szyszka et al. 2009; Kwitter et al. – c9-10: The apparent magnitude and reference. We indicate 1988). A couple of articles that may be useful in identify- the band in which the magnitude is reported. When avail- ing the position of a central star are Kerber et al. (2003) and able, the visual magnitude was preferred. For those objects Chornay & Walton (2020). catalogued as photometric variables, we report an average – c6-9: Spectral classification (SpT) of the CSPNe and refer- ence (t.w. means this work). We use the most current SpTs, 1 http://www.drdjones.net/bCSPN/
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magnitude. For binary systems, it is probable that the re- ported magnitude corresponds to the bright source, which is H-poor 0.10 not necessary the ionizing source. Moreover,when the CSPN H-rich is binary, it is usual that it presents photometric variations. 0.08 The physical parameters that we report in the tables are the 0.06 most up-to-date and post 1982. In addition, we include the un- n certainty, only in cases where the original author published them. Nevertheless, there are objects that undergo a fast evolution of 0.04 their physical parameters. For example He 3−1357 (Reindl et al. 2014a). In this sense, the physical parameters of the CSPN have 0.02 importance from a statistical viewpoint.
0.00 0 10 20 30 40 50 60 70 80 90 4.3. Multiplicity vs. spectral type Galactic latitude CSPNe confirmed to be part of a binary system are described in Table 1 (column 10). It is known that many stars are binary, but Fig. 2. Normalized distributions in Galactic latitude of CSPNe (of con- in few cases it is possible to have the spectrum of the two stars firmed and possible PNe) that belong to H-rich and H-poor group. Each separately. The criterion for describing the spectral type in these bin has a width of 5 deg. cases is S pT1 + S pT2. Where the first star is the brightest, not necessarily the ionizing star of the nebula. In the case in which The physical parameters that we have collected from the lit- + the spectral type of a star is not known,it is indicatedas S pT1 ?. erature allow us to characterize the CSPNe population (Table 3). The fact that recently the number of CSPNe that are binary Although it is generally accepted that hydrogen requires a min- systems have been increased considerably, means that we have imum temperature of 10000 K to ionize, the minimum temper- to rethink which component would be considered the CSPN. An ature of a CSPN is 13000 K. This value agrees with what was appropriate response would be: the star of the binary system re- expected. sponsible for the ionization of the nebula. Nevertheless, it is pos- According to the values presented in Table 3 (Figs. 3, 4, and sible that both stars of the binary system have enough tempera- 5), the H-poor population appears to have grater surface gravity ture to ionize the nebula.This is the case of He 2−428, where the than the H-rich one, except for the most evolved objects. With first star has Te f f =48±7 kk and the second star has Te f f =46±7 regard to the effective temperature, the H-poor group is clearly kk (Reindl et al. 2018). hotter. Luminosity shows a more complex situation. Still a trend Two objects require clarification because there are no can be appreciated in which more evolved H-poor objects dis- references reporting its binarity: i) Cn 1−1: there is evi- play a higher luminosity. dence indicating that this object is a D’-type symbiotic star Moreover, Fig. 6 shows the [WR] subtype distribution, where (Gutierrez-Moreno et al. 1995a). ii) PHR J0905−4753: in the a dearth of objects with subtypes 5-7 is apparent. This feature is MASH cataloguethe central star is identified with a spectral type seen both in our restricted sample with definite spectral types A8. If this is correct, then it is indeed a binary system. (our "pure" sample), as well as in the complete sample that in- cludes also uncertain spectral types. This result is consistent with previous results in the literature Todt (2009). Even more, given 5. Results that our sample is significantly larger than that discussed by Todt (2009), we consider this result as a confirmation that the lack of 5.1. Dichotomy between H rich and poor CSPNe subtypes 5-7 in [WR]-CSPNe is a real feature. In principle this We separate the CSPNe of our sample according to their atmo- gap could be explained in two different ways. On the one hand spheric hydrogen abundance into H-rich and H-poor (see Ta- it could be the consequence of faster evolutionary speeds at that ble 2). The ratio H-rich/H-poor in the present catalogue is 2:1, particular stage and, on the other, it could be the consequence which is greater than the one found by Weidmann & Gamen that specific photospheric conditions are necessary for [WR]- (2011b). Nevertheless, it is still far from the value determined CSPNe to be classified as [WC 5-7]. Interestingly, a concomitant by Mendez (1991). The large number of objects included in our gap is not apparent in the sample of H-deficient CSPNe with de- present catalogue reinforce the idea that the H-poor population rived effective temperatures, suggesting that the latter might be is larger than previously thought. the right explanation. This hypothesis will need to be teste by Applying the Kolmogorov-Smirnov test to compare the specifically tailored future studies. Galactic latitude distributions of H-rich and H-poor populations, Regarding Of-type CSPNe, within these objects early sub- wefindD=0.2 and a p-value=0.00049.This is in agreement with types are predominant,with the coolest object being Hen 2−138, the results found by Weidmann & Gamen (2011b), which im- classified as O(H)7-9 f. Mendez et al. (1990) proposes that O plies that the distribution in Galactic latitudes of H-rich and H- stars are less luminous than the Of stars. However, we do not poor stars are different (Fig. 2). This is an indication that the find a significant difference between both groups. We find that 3 3 progenitors masses and ages of both populations are different. O-type CSPNe have (L⋆/L⊙)=5.3×10 and (L⋆/L⊙)=5.7 ×10 The progenitorsof H-deficient stars expected to be more massive for Of-type. and younger than those of their H-rich counterparts. It would A peculiar situation can be observed by comparing the num- be interesting to analyse whether this can be related to the ob- ber of objects with different spectral types. The number of ob- served dearth of H-deficient white dwarfs in old globular clus- jects classified as [WC 4-12] is larger than [WO 1-4]. We in- ters (Moehler et al. 2004; Davis et al. 2009), as reasons behind terpret this as a difference in evolutionary speeds. i.e., these ob- this feature are still not clear (Williams et al. 2018). jects spend more time in its earliest evolutionary stage than in
Article number, page 5 of 46 A&A proofs: manuscript no. aanda
Table 2. Summary of the spectral types of CSPNe compiled in our cata- Table 3. Average physical parameter of our catalogue. We only included logue, grouped by their atmospheric hydrogen abundance. We include objects with accurate SpT, and exclude objects with confirmed binary confirmed and probable spectral types. Here, we have discarded 6 ob- nucleus. Between parentheses the number of objects is indicated. jects without any specific spectral type.
3 3 H-rich H-poor Population logg Te f f ×10 (L⋆/L⊙) ×10 SpT sampleSpT sampleSpT sample [WC 4-12] 4.17 (33) 50 (41) 6.3 (36) O3-B1 133 cont. 22 [WC4-12] 68 [WO 1-4] 5.37 (20) 110 (23) 4.2 (21) Of 31 hybrid 3 [WO1-4] 37 PG 1159 6.68 (10) 117 (14) 0.7 (13) Of-WR(H) 3 SySt 11 [WN] 8 O8 -B0 3.51 (13) 38 (16) 10 (14) B2-M9 40 Blue 50 [WR] 10 O3-7 4.52 (26) 71 (29) 5.9 (29) DA,WD 14 EL 8 PG1159 17 hgO(H), DA, DAO 6.93 (31) 99 (33) 0.1 (25) DAO 28 wels 77 [WC]-PG1159 2 sdO 12 O(He) 5 hgO(H) 12 O(C) 1
B[e] 6 DO 4 18 H-poor H-rich 11 H-poor 1 H-rich Total 290 Total 171 Total 153 15
Notes. 12 1The O3-B1 group include objects classified as O(H), O and OB.
2 N [WR] group include the two objects classified as [WN/C] and [WO]- 9 [WC 8].
6 the subsequent ones. Interestingly, this is in clear contradiction with what is expected from the late thermal pulse scenario. Stel- 3 lar evolution models are predicted to slow their evolution as they 0 reach their maximum effective temperature (i.e. the "knee" of 2 3 4 5 6 7 8 the evolutionary tracks in the HR-diagram, see the supplemen- log(g) tary material in Guerrero et al. 2018). Alternatively, this could be a consequence of the larger luminosity expected during the earlier stellar evolution, which leads to a larger volume in which Fig. 3. Distribution in surface gravity of CSPNe. these stars can be detected. Volume limited samples are required to solve this issue. On the other hand, the distributions of the O-type CSPNe over the subtypes is different (Fig. 7). This distri- H-poor bution is in general flat, but with a remarkable number of objects 20 H-rich classified as O3. This may be due to a selection effect. Since for the O-type CSPNe the spectral classification is more qualitative that in case of the [WR], many objects have doubtful classifica- 15 tions. But, in the case of the O3 CSPNe, these are easily identi- v N fiable by the absorption of the N . 10 Nevertheless, this might be due to the saturation of a quali- tative classification scheme, originally constructed for main se- quence object, when applied to the much hotter CSPNe. 5 Finally, Figs. 8 and 9 display the distribution of spectral sub- types for both the H-poor and H-rich populations. According to the evolutionary sequence described in Fig. 1, stars are thought 0 2.5 5 7.5 10 12.5 15 17.5 20 to evolve along evolutionary tracks, first increasing their effec- 4 tive temperature and then becoming dimmer and entering the Teff/10 [K] white dwarf cooling sequence. Fig. 4. Distribution in temperature of CSPNe. 5.2. Binary CSPNe While there are continuous efforts focused on the search for new with nine objects that do not have a specific spectral type. In addition, there are 34 objects with late spectral types. binary in PNe (e.g., Douchin et al. 2015), the fraction of PNe with binary nuclei is still relatively small2. In our catalogue there For the vast majority of binary systems there are only spec- are 117 PNe with a confirmed binary system at its nuclei. We do troscopic data for the brightest star, so there are few systems in not include the SySt stars. Eleven of them belong to the H-poor which we know the spectral type of the two stars of the system. ff group ([WR], DO, H-poor, O(He), PG 1159, and [WN]), plus an No binary systems composed by stars with di erent H abun- + object classified as [WR]/wels (Vy 1−2). The O, O(H), O(H)f, dances in its atmosphere (i.e. H-rich H-poor) are currently sdO, H-rich, DAO, and hgO(H) stars totalize 62 objects, together known. In this sense, and for statistical purposes, we adopt the criterion of using the H abundance of the brightest star. 2 A regularly updated catalogue of binary CSPNe is mantained by With the above clarifications, we found that 10.3% of con- David Jones can be found at http://www.drdjones.net/bcspn/. firmed binaries belong to the H-poor group and 82.1% to the H-
Article number, page 6 of 46 Weidmann, et al.: Catalogue of central stars of planetary nebulae