Spectroscopy of Planetary Nebulae in Sextans A and Sextans B

1. 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

2. 1 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) LGC:WFC @ INT

3. 4 5 3 1 2 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) LGC:WFC @ INT

4. Observations: • FORS2 @ VLT • Grisms: 300 V with Texp =5400 s 300 I with Texp =3600 s • Spectral range: ~3500-9600 Å • Dispersion: 3 Å/pixel • S/N > 10 for temperature diagnostic lines

5. H + [NII] 4363 Å [OIII] 6717-6723 Å [SII] 5755 Å [NII] Sextans A spectra:

6. 4363 Å [OIII] H + [NII] H + [NII] [SII] 6717-6731 Å Sextans B spectra:

7. Computing chemical abundances: • With classic Ionization correction factors (ICFs), following Kingsburgh & Barlow (1994) • 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

8. PN in Sextans A: ICFs Cloudy • He/H 0.085 0.085 • O/H 8.0 8.1 • N/H 8.4 8.4 • Ne/H 6.7 6.7 • Ar/H 5.3 5.2 • S/H 5.8 5.8 C   0.2 T[OIII] 21000 K from [OIII] 4363/5007 Å flux ratio T[NII] 13400 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

9. PNe in Sextans B: ICFs Cloudy (average of 5 PNe) • <He/H> 0.081 0.089 • <O/H> 7.9 8.0 • <N/H> <7 <6.5 • <Ne/H> 7.0 7.2 • <Ar/H> 5.6 5.6 • <S/H> - <5.7 C   0.1 T[OIII] from 12500 to 17500 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

10. 8.20 7.99 7.62 7.66 8.00 15 ‘ x 15’ Sextans B:Oxygen abundance

11. 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

12. 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

13. 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.

14. Sextans B PNe: O/H~ 7.62-8.20 (this work) Sextans A O/H~7.98 (this work) 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)

15. 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.

16. 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