2001ApJ...548..288L

Query : 2001ApJ...548..288L

2001ApJ...548..288L - Astrophys. J., 548, 288-295 (2001/February-2)

Photoevaporating flows from the cometary knots in the Helix Nebula (NGC 7293).

LOPEZ-MARTIN L., RAGA A.C., MELLEMA G., HENNEY W.J. and CANTO J.

Abstract (from CDS):

We explain the Hα emission of the cometary knots in the Helix Nebula (NGC 7293) with an analytical model that describes the emission of the head of the globules as a photoevaporated flow produced by the incident ionizing radiation of the central star. We compare these models with the Hα emission obtained from the Hubble Space Telescope (HST) archival images of the Helix Nebula. From a comparison of the Hα emission with the predictions of the analytical model we obtain a rate of ionizing photons from the central star of about 5x1045 s–1, which is consistent with estimates based on the total Hβ flux of the nebula. We also model the tails of the cometary knots as a photoevaporated wind from a neutral shadow region produced by the diffuse ionizing photon field of the nebula. A comparison with the HST images allows us to obtain a direct determination of the value of the diffuse ionizing flux. We compare the ratio of diffuse to direct stellar flux as a function of radius inside an H II region with those obtained from the observational data through the analytical tail and head wind model. The agreement of this model with the values determined from the observations of the knots is excellent.

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Journal keyword(s): ISM: Structure - ISM: Planetary Nebulae: Individual: NGC Number: NGC 7293 - Stars: AGB and Post-AGB

Nomenclature: Table 1: [BO98] Helix SSs-MSS N=20 added.

Simbad objects: 24

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Number of rows : 24
N Identifier Otype ICRS (J2000)
RA 		ICRS (J2000)
DEC 		Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2026 		#notes
1 M 42 HII 05 35 16.8 -05 23 15           ~ 4411 0
2 NAME Ori A MoC 05 38 -07.1           ~ 3187 0
3 [BO98] Helix 351-802 PoC 22 29 35.1 -20 48 02           ~ 1 0
4 [BO98] Helix 352-815 PoC 22 29 35.2 -20 48 15           ~ 4 0
5 [BO98] Helix 352-750 PoC 22 29 35.2 -20 47 50           ~ 1 0
6 [BO98] Helix 354-804 PoC 22 29 35.4 -20 48 04           ~ 2 0
7 [BO98] Helix 360-751 PoC 22 29 36.0 -20 47 51           ~ 3 0
8 [BO98] Helix 363-740 PoC 22 29 36.3 -20 47 40           ~ 1 0
9 [BO98] Helix 372-725 PoC 22 29 37.2 -20 47 25           ~ 1 0
10 [BO98] Helix 378-801 PoC 22 29 37.8 -20 48 01           ~ 17 0
11 NGC 7293 PN 22 29 38.5454047152 -20 50 13.747242408 11.894 13.158 13.524 13.689 13.898 DAO.5 983 1
12 [BO98] Helix 386-749 PoC 22 29 38.6 -20 47 50           ~ 3 0
13 [BO98] Helix 389-742 PoC 22 29 38.9 -20 47 42           ~ 1 0
14 [BO98] Helix 398-752 PoC 22 29 39.8 -20 47 52           ~ 4 0
15 [BO98] Helix 410-808 PoC 22 29 41.0 -20 48 08           ~ 1 0
16 [BO98] Helix 413-818 PoC 22 29 41.3 -20 48 18           ~ 1 0
17 [BO98] Helix 425-822 PoC 22 29 42.5 -20 48 22           ~ 1 0
18 [BO98] Helix 428-827 PoC 22 29 42.8 -20 48 27           ~ 2 0
19 [BO98] Helix 459-905 PoC 22 29 45.9 -20 49 05           ~ 3 0
20 [BO98] Helix 465-853 PoC 22 29 46.5 -20 48 53           ~ 1 0
21 [BO98] Helix 473-919 PoC 22 29 47.3 -20 49 19           ~ 1 0
22 [BO98] Helix 473-931 PoC 22 29 47.4 -20 49 31           ~ 3 0
23 [BO98] Helix 480-925 PoC 22 29 48.0 -20 49 25           ~ 1 0
24 [BO98] Helix 494-911 PoC 22 29 49.4 -20 49 11           ~ 1 0

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