- ID:
- ivo://CDS.VizieR/J/A+A/373/1032
- Title:
- Radio emission from planetary nebulae
- Short Name:
- J/A+A/373/1032
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have analysed the radio fluxes for 264 planetary nebulae for which reliable measurements of fluxes at 1.4 and 5 GHz, and of nebular diameters are available. For many of the investigated nebulae, the optical thickness is important, especially at 1.4 GHz. Simple models like the one specified only by a single optical thickness or spherical, constant density shells do not account satisfactorily for the observations. Also an r^-2^ density distribution is ruled out. A reasonable representation of the observations can be obtained by a two-component model having regions of two different values of optical thickness. We show that the nebular diameters smaller than 10" are uncertain, particularly if they come from photographic plates or Gaussian fitting to the radio profile. While determining the interstellar extinction from an optical to radio flux ratio, caution should be paid regarding optical thickness effects in the radio. We have developed a method for estimating the value of self absorption. At 1.4 GHz self absorption of the flux is usually important and can exceed a factor of 10. At 5 GHz self absorption is negligible for most of the objects, although in some cases it can reach a factor of 2. The Galactic bulge planetary nebulae when used to calibrate the Shklovsky method give a mean nebular mass of 0.14M_{sun}_. The statistical uncertainty of the Shklovsky distances is smaller than a factor of 1.5.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/681/1296
- Title:
- Radio evolution of the PN NGC 7027
- Short Name:
- J/ApJ/681/1296
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- 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_{sun}_ adopting the Blocker stellar evolution models, or about 0.04M_{sun}_ 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.
- ID:
- ivo://CDS.VizieR/J/ApJS/159/282
- Title:
- 315 radio identified planetary nebulae
- Short Name:
- J/ApJS/159/282
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using the 1.4GHz NRAO VLA Sky Survey (NVSS, Cat. <VIII/65>) images and source catalog, we identified 315 radio sources stronger than ~2.5mJy among over 1000 recently discovered planetary nebulae north of J2000 declination {delta}=-40{deg}. Two-thirds of these radio sources are weaker than 10mJy at 1.4GHz. This result is a uniform supplement to the previous NVSS radio identification of known PNe and a large homogeneous sample including over 1000 PNe with NVSS sources is obtained. By examining the radio properties of PNe, it is found that most of the planetary nebulae detected at both 1.4 and 5.0GHz are optically thick at {lambda}=20cm.
- ID:
- ivo://CDS.VizieR/J/A+A/274/895
- Title:
- Radio observations of South. PN Candidates
- Short Name:
- J/A+A/274/895
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- IRAS sources having IR colours typical of planetary nebulae and located outside the Galactic bulge were observed in the radio continuum at 6cm with the Australian Compact Array (ACA). 18 new planetary nebulae were discovered among 89 candidates. The observations were performed in March and April 1991.
- ID:
- ivo://CDS.VizieR/J/A+AS/142/85
- Title:
- Recombination coefficients for C II lines
- Short Name:
- J/A+AS/142/85
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Effective recombination coefficients are given for C II transitions between doublet states. The calculations are carried out in the temperature range 500-20000K and for an electron density of 10^4^cm^-3^. The effects of electron collisions on the excited states are included. The necessary bound-bound and bound-free radiative data are obtained from a new R-matrix calculation in which photoionization resonances are fully delineated, thereby accurately incorporating the effects of both radiative and dielectronic recombination. The R-matrix calculation includes all bound states with principal quantum number n<=15 and total orbital angular momentum L<=4. The effect of moving the resonance features to their experimentally determined positions is also investigated and found to be important at low temperatures.
- ID:
- ivo://CDS.VizieR/J/ApJS/157/371
- Title:
- Recombination lines in planetary nebulae
- Short Name:
- J/ApJS/157/371
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Recombination lines (RLs) of C II, N II, and O II in planetary nebulae (PNs) have been found to give abundances that are much larger in some cases than abundances from collisionally excited forbidden lines (CELs). The origins of this abundance discrepancy are highly debated. We present new spectroscopic observations of O II and C II recombination lines for six planetary nebulae.
- ID:
- ivo://CDS.VizieR/J/A+A/476/1019
- Title:
- RMS survey of southern candidate massive YSOs
- Short Name:
- J/A+A/476/1019
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Red MSX Source (RMS) survey is an ongoing effort to return a large, well-selected sample of massive young stellar objects (MYSOs) within our Galaxy. 2000 candidates have been colour-selected from the Mid-course Space Experiment (MSX) point source catalogue (PSC). A series of ground-based follow-up observations are being undertaken in order to remove contaminant objects (ultra-compact HII (UCHII) regions, planetary nebulae (PN), evolved stars), and to begin characterising these MYSOs. As a part of these follow-up observations, high resolution (~1") mid-IR imaging aids the identification of contaminant objects which are resolved (UCHII regions, PN) as opposed to those which are unresolved (YSOs, evolved stars) as well as identifying YSOs near UCHII regions and other multiple sources. We present 10.4{mu}m imaging observations for 346 candidate MYSOs in the RMS survey in the Southern Hemisphere, primarily outside the region covered by the GLIMPSE Spitzer Legacy Survey. These were obtained using TIMMI2 on the ESO 3.6m telescope in La Silla, Chile. Our photometric accuracy is of order 0.05Jy, and our astrometric accuracy is 0.8", which is an improvement over the nominal 2" accuracy of the MSX PSC.
- ID:
- ivo://CDS.VizieR/II/229
- Title:
- Sakurai's object (V4334 Sgr) in 1996-1998
- Short Name:
- II/229
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The photometric UBV observations of V4334 Sgr during 1996-1998 are presented. V4334 Sgr is the nucleus of a planetary nebula during the last helium flash of the shell source and it entered the R CrB phase.
- ID:
- ivo://CDS.VizieR/J/A+A/655/A46
- Title:
- Simulated IR spectra of PN Hubble 12
- Short Name:
- J/A+A/655/A46
- Date:
- 10 Mar 2022 07:09:39
- Publisher:
- CDS
- Description:
- We present a visible-infrared imaging study of young planetary nebula (PN) Hubble 12 (Hb 12; PN G111.8-02.8) obtained with Hubble Space Telescope (HST) archival data and our own Canada-France-Hawaii Telescope (CFHT) measurements. Deep HST and CFHT observations of this nebula reveal three pairs of bipolar structures and an arc-shaped filament near the western waist of Hb 12. The existence of nested bipolar lobes together with the presence of H2 knots suggests that these structures originated from several mass-ejection events during the pre-PN phase. To understand the intrinsic structures of Hb 12, a three-dimensional model enabling the visualisation of this PN at various orientations was constructed. The modelling results show that Hb 12 may resemble other nested hourglass nebulae, such as Hen 2-320 and M 2-9, suggesting that this type of PN may be common and the morphologies of PNs are not so diverse as is shown by their visual appearances. The infrared spectra show that this PN has a mixed chemistry. We discuss the possible material that may cause the unidentified infrared emissions. The analyses of the infrared spectra and the spectral energy distribution suggest the existence of a cool companion in the nucleus of this object.
- ID:
- ivo://CDS.VizieR/J/A+AS/127/185
- Title:
- SiO masers in OH/IR stars, proto-PN and PN
- Short Name:
- J/A+AS/127/185
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a search for SiO masers towards a sample of 126 objects including OH/IR stars, proto-planetary and planetary nebulae. All objects are classified as oxygen-rich, and most of them are associated with OH or H_2_O masers. SiO masers were found only in variable objects like the OH/IR stars and a few objects classified as proto-planetary nebulae, but with variable central stars that may be part of binary systems. In one object, OH 15.7+0.8, which appears to be varying irregularly and most likely recently left the AGB, an SiO maser was tentatively detected. Thus, we conclude that variability and SiO maser emission are closely linked, and that SiO masers disappear very soon after a star has reached the end of the AGB, when pulsation and mass loss cease.
