Spectroscopy of southern Galactic disk planetary nebulae. Notes on chemical composition and emission-line stars

We present low resolution spectroscopic observations for a sample of 53 planetary nebulae (PNe) located in the southern sky between Vela and Norma constellations and pertaining to the Galactic disk with expected Galactocentric distance range of 5 to 10 kpc. We derive nebular chemical composition and plasma parameters with the classical empirical method. For most of the observed objects, this has been done for the first time. The distributions of the chemical abundances of the observed disk sample are generally indistinguishable from Galactic bulge and inner-disk PNe populations. The exceptions are possible differences in the He/H distribution, as compared to bulge PNe and Ne/Ar, compared to inner-disk PNe sample. The derived O/H ratios for the observed disk PNe fit to the concept of flattening of the chemical gradient in the inner parts of the Milky Way. We use the spectra to search for emission-line central stars in the observed sample. We found 6 new emission-line central stars comprising examples of all known types: WEL, VL and [WR]. We confirm that these types represent three evolutionary unconnected forms of enhanced mass-loss in the central stars of PNe. We note on the problem of high ionisation PNe with nebular CIV emission that can mimic the presence of WEL central stars in 1D spectra.Comment: 35 pages, 19 figures, 4 tables (Note: corrected error in measured flux of [O II] 7325 lines in Table B.1

The evolving spectrum of the planetary nebula Hen 2-260

We analysed the planetary nebula Hen 2-260 using optical spectroscopy and photometry. We compared our observations with the data from literature to search for evolutionary changes. The nebular line fluxes were modelled with the Cloudy photoionization code to derive the stellar and nebular parameters. The planetary nebula shows a complex structure and possibly a bipolar outflow. The nebula is relatively dense and young. The central star is just starting $\rm O^+$ ionization ($\rm T_{eff} \approx 30,000 \, K$). Comparison of our observations with literature data indicates a 50% increase of the [OIII] 5007 \AA\ line flux between 2001 and 2012. We interpret it as the result of the progression of the ionization of $\rm O^{+}$. The central star evolves to higher temperatures at a rate of $\rm 45 \pm 7\,K\, yr^{-1}$. The heating rate is consistent with a final mass of $\rm 0.626 ^{+0.003}_{-0.005} \, M_{\odot}$ or $\rm 0.645 ^{+0.008}_{-0.008} \, M_{\odot}$ for two different sets of post-AGB evolutionary tracks from literature. The photometric monitoring of Hen 2-260 revealed variations on a timescale of hours or days. The variability may be caused by pulsations of the star. The temperature evolution of the central star can be traced using spectroscopic observations of the surrounding planetary nebula spanning a timescale of roughly a decade. This allows us to precisely determine the stellar mass, since the pace of the temperature evolution depends critically on the core mass. The kinematical age of the nebula is consistent with the age obtained from the evolutionary track. The final mass of the central star is close to the mass distribution peak for central stars of planetary nebulae found in other studies. The object belongs to a group of young central stars of planetary nebulae showing photometric variability.Comment: accepted for publication in A&

Planetary nebulae in the direction of the Galactic bulge: On nebulae with emission-line central stars

We present a homogeneous set of spectroscopic measurements secured with 4-meter class telescopes for a sample of 90 planetary nebulae (PNe) located in the direction of the Galactic bulge. We derive their plasma parameters and chemical abundances. For half of the objects this is done for the first time. We discuss the accuracy of these data and compare it with other recently published samples. We analyze various properties of PNe with emission-line central stars in the Galactic bulge. Investigating the spectra we found that 7 of those PNe are ionized by Wolf-Rayet ([WR]) type stars of the very late (VL) spectral class [WC 11] and 8 by weak emission-line (WEL) stars. From the analysis we conclude that the PN central stars of WEL, VL and remaining [WR] types form three, evolutionary unconnected forms of enhanced mass-loss among central stars of PNe. [WR] PNe seem to be intrinsically brighter than other PNe. Overall, we find no statistically significant evidence that the chemical composition of PNe with emission-line central stars is different from that of the remaining Galactic bulge PNe.Comment: 19 pages, 23 figures, 16 pages of online material, A&A in pres

VLT/UVES spectroscopy of V4332 Sagittarii in 2005: The best view on a decade-old stellar-merger remnant

V4332 Sgr is a red transient (red nova) whose eruption was observed in 1994. The remnant of the eruption shows a unique optical spectrum: strong emission lines of atoms and molecules superimposed on an M-type stellar spectrum. The stellar-like remnant is presumably embedded in a disc-like dusty envelope seen almost face-on. The observed optical spectrum is assumed to result from interactions of the central-star radiation with dust and gas in the disc and outflows initiated in 1994. We reduced and measured a high-resolution (R = ~40 000) spectrum of V4332 Sgr obtained with VLT/UVES in April/May 2005. The spectrum comes from the ESO archives and is the best quality spectrum of the object ever obtained. We identified and measured over 200 emission features belonging to 11 elements and 6 molecules. The continuous, stellar-like component can be classified as ~M3. The interstellar reddening was estimated to be 0.35 < E(B-V) < 0.75. From radial velocities of interstellar absorption features in the NaI D lines, we estimated a lower limit of ~5.5 kpc to the distance of V4332 Sgr. The spectrum of V4332 Sgr considerably evolved between 2005 and 2009. The object significantly faded in the optical, which resulted from cooling of the main remnant by 300-350 K, corresponding to its spectral-type change from M3 to M5-6. The object increased in luminosity by ~50%, however, implying a significant expansion of its dimensions. Most of the emission features seen in 2005 significantly faded or even disappeared from the spectrum of V4332 Sgr in 2009. These resulted from fading of the optical central-star radiation and a decrease of the optical thickness of the cirumstellar matter. V4332 Sgr bears several resemblances to V1309 Sco, which erupted in 2008. This can indicate a similar nature of the eruptions of the two objects. The outburst resulted from merger of a contact binary in V1309 Sco.Comment: A&A in pres

The populations of planetary nebulae in the direction of the Galactic bulge

We have observed 44 planetary nebulae (PNe) in the direction of the Galactic bulge, and merged our data with published ones. We have distinguished, in the merged sample of 164 PNe, those PNe most likely to prtain physically to the Galactic bulge and those most likely to belong to the Galactic disk. We have determined the chemical composition of all the 164 objects in a coherent way. We looked for stellar emission features and discovered 14 new [WR] stars and 15 new weak emission line central stars. The analyzed data led us to the following conclusions: (1) The spectral type distribution of [WR] stars is very different in the bulge and in the disk of the Galaxy. However, the observed distributions are strongly dependent on selection effects. (2) The proportion of [WR] PNe is significantly larger in the bulge than in the disk. (3) The oxygen abundances in [WR] stars do no appear to be significantly affected by nucleosynthesis and mixing in the progenitors. (4) The O/H gradient of the Galactic disk PNe population flattens in the most internal parts of the Galaxy. (5) The median oxygen abundance in the bulge PN population is larger by 0.2 dex than in the disk population seen in the direction of the bulge. (6) Bulge PNe with smaller O/H tend to have smaller radial velocities. (7) The oxygen abundance distribution of bulge PNe is similar in shape to that of the metallicity distribution of bulge giants, but significantly narrower. (8) The location of SB 32 (PN G 349.7-09.1) in the (V_lsr, l_II) diagram and its low oxygen abundance argues that it probably belongs to the halo population.Comment: 14 pages, 16 figures. Accepted for publication in A&

New groups of planetary nebulae with peculiar dust chemistry towards the Galactic bulge

We investigate Galactic bulge planetary nebulae without emission-line central stars for which peculiar infrared spectra have been obtained with the Spitzer Space Telescope, including the simultaneous signs of oxygen and carbon based dust. Three separate sub-groups can be defined characterized by the different chemical composition of the dust and the presence of crystalline and amorphous silicates. We find that the classification based on the dust properties is reflected in the more general properties of these planetary nebulae. However, some observed properties are difficult to relate to the common view of planetary nebulae. In particular, it is challenging to interpret the peculiar gas chemical composition of many analyzed objects in the standard picture of the evolution of planetary nebulae progenitors. We confirm that the dual-dust chemistry phenomenon is not limited to planetary nebulae with emission-line central stars.Comment: 17 pages, 13 figure

Angular dimensions of planetary nebulae

We have measured angular dimensions of 312 planetary nebulae from their images obtained in Halpha (or Halpha + [NII]). We have applied three methods of measurements: direct measurements at the 10% level of the peak surface brightness, Gaussian deconvolution and second-moment deconvolution. The results from the three methods are compared and analysed. We propose a simple deconvolution of the 10% level measurements which significantly improves the reliability of these measurements for compact and partially resolved nebulae. Gaussian deconvolution gives consistent but somewhat underestimated diameters compared to the 10% measurements. Second-moment deconvolution gives results in poor agreement with those from the other two methods, especially for poorly resolved nebulae. From the results of measurements and using the conclusions of our analysis we derive the final nebular diameters which should be free from systematic differences between small (partially resolved) and extended (well resolved) objects in our sample.Comment: 10 figures, 2 table

Planetary nebulae with emission-line central stars

The kinematic structure of a sample of planetary nebulae, consisting of 23 [WR] central stars, 21 weak emission line stars (wels) and 57 non-emission line central stars, is studied. The [WR] stars are shown to be surrounded by turbulent nebulae, a characteristic shared by some wels but almost completely absent from the non-emission line stars. The fraction of objects showing turbulence for non-emission-line stars, wels and [WR] stars is 7%, 24% and 91%, respectively. The [WR] stars show a distinct IRAS 12-micron excess, indicative of small dust grains, which is not found for wels. The [WR]-star nebulae are on average more centrally condensed than those of other stars. On the age-temperature diagram, the wels are located on tracks of both high and low stellar mass, while [WR] stars trace a narrow range of intermediate masses. Emission-line stars are not found on the cooling track. One group of wels may form a sequence wels--[WO] stars with increasing temperature. For the other groups both the wels and the [WR] stars appear to represent several, independent evolutionary tracks. We find a discontinuity in the [WR] stellar temperature distribution and suggest different evolutionary sequences above and below the temperature gap. One group of cool [WR] stars has no counterpart among any other group of PNe and may represent binary evolution. A prime factor distinguishing wels and [WR] stars appears to be stellar luminosity. We find no evidence for an increase of nebular expansion velocity with time.Comment: 14 pages, 9 figures, accepted to A&