2003A&A...400..161B


Query : 2003A&A...400..161B

2003A&A...400..161B - Astronomy and Astrophysics, volume 400, 161-183 (2003/3-2)

The 3-D ionization structure of NGC 6818: A Planetary Nebula threatened by recombination.

BENETTI S., CAPPELLARO E., RAGAZZONI R., SABBADIN F. and TURATTO M.

Abstract (from CDS):

Long-slit NTT+EMMI echellograms of NGC 6818 (the Little Gem) at nine equally spaced position angles, reduced according to the 3-D methodology introduced by Sabbadin et al. (2000A&A...355..688S, 2000A&A...361.1112S), allowed us to derive: the expansion law, the diagnostics and ionic radial profiles, the distance and the central star parameters, the nebular photo-ionization model, the 3-D reconstruction in He II, [O III] and [N II], the multicolor projection and a series of movies. The Little Gem results to be a young (3500 years), optically thin (quasi-thin in some directions) double shell (Mion≃0.13M) at a distance of 1.7kpc, seen almost equatorial on: a tenuous and patchy spherical envelope (r≃0.090pc) encircles a dense and inhomogeneous tri-axial ellipsoid (a/2≃0.077pc, a/b≃1.25, b/c ≃1.15) characterized by a hole along the major axis and a pair of equatorial, thick moustaches. NGC 6818 is at the start of the recombination phase following the luminosity decline of the 0.625 M central star, which has recently exhausted the hydrogen shell nuclear burning and is rapidly moving toward the white dwarf domain (logT*≃5.22K; logL*/L≃3.1). The nebula is destined to become thicker and thicker, with an increasing fraction of neutral, dusty gas in the outermost layers. Only over some hundreds of years the plasma rarefaction due to the expansion will prevail against the slower and slower stellar decline, leading to a gradual re-growing of the ionization front. The exciting star of NGC 6818 (mV≃17.06) is a visual binary: a faint, red companion (mV≃17.73) appears at 0.09arcsec in PA =190°, corresponding to a separation ≥150AU and to an orbital period ≥1500 years.

Abstract Copyright:

Journal keyword(s): planetary nebulae: individual: NGC 6818 - ISM: kinematics and dynamics

Simbad objects: 27

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Number of rows : 27
N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2021
#notes
1 NGC 40 PN 00 13 01.0170260109 +72 31 19.032886305   11.63 11.46     [WC8] 595 2
2 PN Hu 1-1 PN 00 28 15.435 +55 57 54.48           ~ 156 1
3 NGC 1501 PN 04 06 59.3919688584 +60 55 14.277444117   15.17 13.0     [WO4] 284 1
4 IC 418 PN 05 27 28.2060343141 -12 41 50.282659007   9.78 13.0     O7fp 1006 2
5 NGC 2392 PN 07 29 10.7669120392 +20 54 42.478515772     9.68     O6f 703 1
6 NGC 3132 PN 10 07 01.7655812249 -40 26 11.138949314   10.14 10.01     A2V 374 1
7 PN My 59 PN 10 23 09.1339166398 -60 32 42.127143375           O(H)7-9I 122 0
8 NGC 3242 PN 10 24 46.1335198512 -18 38 32.294434711   11.83 12.15     ~ 806 1
9 NGC 4071 PN 12 04 14.7008784506 -67 18 36.459587192     14.00     ~ 87 0
10 PN MyCn 18 PN 13 39 35.0560904148 -67 22 51.758576199   13.30 12.54 13.19 12.61 ~ 269 1
11 PN Mz 3 PN 16 17 13.3911453557 -51 59 10.706640574   10.8 14.00     O9.5 337 0
12 NGC 6153 PN 16 31 30.5709136856 -40 15 12.646146874   10.7 15.55     ~ 291 0
13 NGC 6210 PN 16 44 29.5195973291 +23 47 59.491267229   12.3 11.7     Of/[WR] 576 0
14 NGC 6326 PN 17 20 46.252 -51 45 15.17   12.83 11.53 16.00 15.16 O(H)5-8((fc)) 139 0
15 IC 4663 PN 17 45 28.6294985056 -44 54 17.982999895           [WN3] 93 0
16 NGC 6543 PN 17 58 33.4042519454 +66 37 58.748961810   11.09 11.28     [WC] 1134 1
17 NGC 6565 PN 18 11 52.558 -28 10 42.35   12.5 12.2 12.12   PN 221 0
18 NGC 6751 PN 19 05 55.5385116189 -05 59 32.291075445   15.78 15.48     [WC4] 321 0
19 NGC 6818 PN 19 43 58.022 -14 09 13.44     9.3     ~ 339 1
20 NGC 6826 PN 19 44 48.1500835472 +50 31 30.250916761   10.21 9.6     O6fp 704 0
21 NGC 6884 PN 20 10 23.6401227444 +46 27 39.547818788   11.9 10.9     ~ 308 1
22 PN K 3-57 PN 20 12 47.725 +34 20 32.79           ~ 35 0
23 PN A66 70 PN 20 31 33.2076232587 -07 05 18.032014887           D+G8IV-V 77 0
24 NGC 7009 PN 21 04 10.8153350719 -11 21 48.581808296   12.48 12.07     ~ 972 1
25 PN M 2-51 PN 22 16 03.890 +57 28 33.75           ~ 77 0
26 NGC 7354 PN 22 40 19.8738736066 +61 17 08.744408285           ~ 268 2
27 NGC 7662 PN 23 25 53.6 +42 32 06   9.4 12     ~ 913 0

    Equat.    Gal    SGal    Ecl

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2021.07.25-17:30:14

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