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J/ApJ/681/1296       Radio evolution of the PN NGC 7027       (Zijlstra+, 2008)

The evolution of NGC 7027 at radio frequencies: a new determination of the distance and core mass. Zijlstra A.A., van Hoof P.A.M., Perley R.A. <Astrophys. J., 681, 1296-1309 (2008)> =2008ApJ...681.1296Z
ADC_Keywords: Planetary nebulae ; Radio continuum Keywords: planetary nebulae: individual (NGC 7027) - radio continuum: ISM - stars: AGB and post-AGB - stars: evolution - white dwarfs Abstract: We present the results of a 25yr program to monitor the radio flux evolution of the planetary nebula NGC 7027. We find significant evolution of the spectral flux densities. The flux density at 1465MHz, where the nebula is optically thick, is increasing at a rate of 0.251±0.015%/yr, caused by the expansion of the ionized nebula. At frequencies where the emission is optically thin, the spectral flux density is changing at a rate of -0.145±0.005%/yr, caused by a decrease in the number of ionizing photons coming from the central star. A distance of 980±100pc is derived. By fitting interpolated models of post-AGB evolution to the observed changes, we find that over the 25yr monitoring period, the stellar temperature has increased by 3900±900K and the stellar bolometric luminosity has decreased by 1.75±0.5%. We derive a distance-independent stellar mass of 0.655±0.010M adopting the Blocker stellar evolution models, or about 0.04M higher when using models of Vassiliadis & Wood. A Cloudy photoionization model is used to fit all epochs at all frequencies simultaneously. The differences between the radio flux density predictions and the observed values show some time-independent residuals of typically 1%. A possible explanation is inaccuracies in the radio flux scale of Baars and coworkers. We propose an adjustment to the flux density scale of the primary radio flux calibrator 3C 286, based on the Cloudy model of NGC 7027. We also calculate precise flux densities for NGC 7027 for all standard continuum bands used at the VLA, as well as for some new 30 GHz experiments. Description: NGC 7027 has been observed at the VLA over a 25yr period. Data were obtained for 12 epochs between 1983 and 2006. The available data, along with the estimated uncertainties, are summarized in Table 1, as ratios between NGC 7027 and 3C 286. Objects: -------------------------------------------------------------- RA (2000) DE Designation(s) -------------------------------------------------------------- 21 07 01.6 +42 14 10 NGC 7027 = PN G084.9-03.4 13 31 08.3 +30 30 33 3C 286 = FIRST J133108.2+303032 -------------------------------------------------------------- File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table6.dat 24 171 Model flux densities for NGC 7027 table1.dat 129 12 *NGC 7027/3C 286 flux density ratios, with uncertainties
Note on table1.dat: Flux densities for NGC 7027 can be calculated using the Baars flux density scale (in Jy) for 3C 286, as follows: 15.52 at 1275MHz, 14.51 at 1465MHz, 7.758 at 4535MHz, 7.410 at 4885MHz, 5.189 at 8435MHz, 5.066 at 8735MHz, 3.455 at 14965MHz, 2.560 at 22460MHz and 1.537 at 43340MHz. See table 2 for more details.
See also: J/A+A/442/249 : Integrated spectrum of NGC 7027 (Zhang+, 2005) J/A+A/303/175 : Line spectrum of NGC 7027 (Baluteau+, 1995) Byte-by-byte Description of file: table6.dat
Bytes Format Units Label Explanations
1- 9 F9.6 GHz Freq Frequency 11- 17 F7.2 mJy Flux NGC 7027 model flux density for epoch 2000.0 19- 24 F6.3 mJy/yr SecVar Secular variation of the flux density
Byte-by-byte Description of file: table1.dat
Bytes Format Units Label Explanations
1- 7 F7.2 --- Epoch Epoch (in decimal years) 9- 15 F7.5 --- R1275 ? NGC 7027/3C 286 flux density ratio at 1275MHz 17- 23 F7.5 --- e_R1275 ? R1275MHz uncertainty 25- 31 F7.5 --- R1465 NGC 7027/3C 286 flux density ratio at 1465MHz 33- 39 F7.5 --- e_R1465 R1465MHz uncertainty 41- 46 F6.4 --- R4535 ? NGC 7027/3C 286 flux density ratio at 4535MHz 48- 53 F6.4 --- e_R4535 ? R4535MHz uncertainty 55- 60 F6.4 --- R4885 NGC 7027/3C 286 flux density ratio at 4885MHz 62- 67 F6.4 --- e_R4885 R4885MHz uncertainty 69- 73 F5.3 --- R8435 ? NGC 7027/3C 286 flux density ratio at 8435MHz 75- 79 F5.3 --- e_R8435 ? R8435MHz uncertainty 81- 86 F6.4 --- R8735 ? NGC 7027/3C 286 flux density ratio at 8735MHz 88- 93 F6.4 --- e_R8735 ? R8735MHz uncertainty 95-100 F6.4 --- R14965 NGC 7027/3C 286 flux density ratio at 14965MHz 102-107 F6.4 --- e_R14965 R14965MHz uncertainty 109-113 F5.3 --- R22460 NGC 7027/3C 286 flux density ratio at 22460MHz 115-119 F5.3 --- e_R22460 R22460MHz uncertainty 121-124 F4.2 --- R43340 ? NGC 7027/3C 286 flux density ratio at 43340MHz 126-129 F4.2 --- e_R43340 ? R43340MHz uncertainty
History: From electronic version of the journal
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 02-Nov-2010
The document above follows the rules of the Standard Description for Astronomical Catalogues.From this documentation it is possible to generate f77 program to load files into arrays or line by line

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