Spectroscopy of Planetary Nebulae in Sextans A and Sextans B Laura Magrini (1), Mario Perinotto (1), Pierre Leisy (2, 3), Romano L.M. Corradi (2), Antonio Mampaso (3), Jose’ Vilchez (4) (1) Dipartimento di Astronomia, Universita' di Firenze (Italy) (2) ING, La Palma (Spain) (3) IAC, Tenerife (Spain) (4) IAA, Spain

Sextans A Type Ir V Distance 1.45 Mpc (Sakai et al. 1996) 12+log(O/H)=7.49 form HII regions spectra (Skillman et al. 1989) Number of PNe: 1 (Jacoby & Lesser 1981, Magrini et at. 2003) 1 INT

Sextans B Ir IV-V Distance 1.32 Mpc (Sakai et al. 1997) 12 + log (O/H)=7.56 from HII regions (Skillman et al. 1989) Number of PNe: 5 (Magrini et al. 2002) INT

Observations: VLT Grisms: 300 V with T exp =5400 s 300 I with T exp =3600 s Spectral range: ~ Å Dispersion: 3 Å/pixel S/N > 10 for temperature diagnostic lines

Sextans A spectra: 4363 Å [OIII] 5755 Å [NII] Å [SII] H  + [NII]

Sextans B spectra: 4363 Å [OIII] H  + [NII] [SII] Å H  + [NII]

Computing chemical abundances: With CLOUDY 94.00, modeling our PNe in the simplest way: Blackbody central stars with effective temperature derived using the Ambartsumian’s (1932) or Gurzadyan’s (1988) methods Spherical nebula with constant density (derived from [SII] 6717/6731 Å flux ratio when available) Further iterations: Central star luminosity set to match the observed [OIII] 5007 Å flux Nebular radius is varied to adjust predicted low ionization emission lines (i.e. [OII] 3727 Å) with the observed ones Chemical abundances are varied to match observed emission line fluxes With classic Ionization correction factors ( ICFs ), following Kingsburgh & Barlow (1994)

PN in Sextans A: ICFs Cloudy He/H O/H N/H Ne/H Ar/H S/H C   0.2 T[OIII] K from [OIII] 4363/5007 Å flux ratio T[NII] K from [NII] 5755/6584 Å Ne 2700 cm -3 from [SII] 6717/6731 Å From CLOUDY model: T  : 190,000 K logL  : 3.8 L  Radius of the nebula : 0.13 pc

PNe in Sextans B: ICFs Cloudy (average of 5 PNe) <7< <5.7 C   0.1 T[OIII] from to K from [OIII] 4363/5007 Å T[NII] assumed equal to T[OIII] Ne assumed 3000 cm -3 From CLOUDY model: T  : from 60,000 to 80,000 K logL  3.0 to 3.4 L  Radii of the nebulae: form 0.01 to 0.07 pc

Sextans B:Oxygen abundance ‘ x 15’

Evolutionary tracks:  H-burning tracks  SexA PN central star: ~0.68 M  from MS star ~2.5 M   SexB PNe central stars: ~0.57 to ~0.59 M  from MS stars ~1-1.5 M 

Physico-Chemical parameters: He/H vs N/O

O/H vs Ne/H Strong linear relation between O/H and Ne/H (cf. Kaler; Henry 1989). Sex A and Sex B PNe follow this “universal” relation within the uncertainties

N/H vs. N/O The correlation N/H vs N/O (e.g. Henry 1990), suggests that the increase in N/O with N/H is primarily due to the increase of N and not to changes in O abundance.

O/H vs N/O No evident anti- correlation considering all Pne population. A possible anti- correlation if we take in account only Pne with log(N/O) > -0.3, i.e. Type I, for which N can be produced partially by ON cycle.

PNe vs HII regions abundances: Sextans B HII regions: O/H~8.11 (Moles et al.1990); 7.56 (Skillman et al.1989) 7.86 (Pilyugin 2001) Sextans A O/H~7.49 (Skillman et al. 1989) 7.71 (Pilyugin 2001) 8.1 (this work) Sextans B PNe: O/H~ (this work) Sextans A O/H~7.98 (this work)

Luminosity-metallicity relationship in the Local Group Binggeli (1994), Mateo (1998) suggest a bimodal behaviour in luminosity- metallicity relationship between dSph and dIrr. This behaviour is more evident if consider an uniform determination of O/H, as using PNe, which are present in every morphological type of galaxy.

Chemical abundances in the LG from PNe galaxy D (kpc) He/HN/HO/HNe/HS/HAr/HRef. MW Kingsburgh & Barlow 1994 Sag Df Walsh et al LMC Leisy et al SMC Leisy et al Fornax Maran et al NGC Leisy, this congress NGC Richer &McCall 1995 NGC Richer &McCall 1995 LeoA Skillman et al.1989 M Stasinska et al M Jacoby & Ciardullo 1999 M Magrini et al. subm. Sextans A This work Sextans B < <5.75.6This work

Conclusions: Deep spectroscopy of 5 PNe in Sex B and 1 in Sex A with VLT PN in Sex A: the farthest PN (1.45 Mpc) with both [NII] and [OIII] electron temperatures measured Chemical abundances with ICFs and CLOUDY