Skinner et al. presented two high-resolution 6-cm (5 GHz) images of the B-supergiant star P Cygni. These show the observed morphology and flux densities to have changed over the intervening month. ...Following on from this, we present a series of seven high-resolution 6-cm images (including re-reductions of the two from Skinner et al.). These confirm that radio emission from the inner 400 mas of the wind is inhomogeneous, consisting usually of several separated bright spots, and that the total and peak flux densities and the observed morphology vary over all time-scales sampled. We suggest that recombination in cooling clumps of gas which will decrease the radio emission, followed by the appearance of other ionized clumps, could explain such rapid changes, but detailed models must await further observations.
CAL 83 is a prototype of the class of Super Soft X-ray Sources (SXS). It is a binary consisting of a low mass secondary that is transferring mass onto a white dwarf primary and is the only known SXS ...surrounded by an ionisation nebula, made up of the interstellar medium (ISM) ionised by the source itself. The authors study this nebula using integral field spectroscopy. They can use these data to compare to models of how CAL 83 should ionise its surroundings, based on what they know about the source emission spectrum and the physical conditions of the surrounding ISM. CAL 83 appears to have a fairly standard ionisation nebula as far as the morphology goes: the edges where H is recombining are strong in the low stage ionisation lines and the central, clumpy regions are stronger in the higher stage ionisation lines. In particular, the authors wish to know if the He II emission and the other nebular lines are powered by the same ionising source.
Aims. We report the first detections of OH+ emission in planetary nebulae (PNe). Methods. As part of an imaging and spectroscopy survey of 11 PNe in the far-IR using the PACS and SPIRE instruments ...aboard the Herschel Space Observatory, we performed a line survey in these PNe over the entire spectral range between 51 mu m and 672 mu m to look for new detections. Results. The rotational emission lines of OH+ at 152.99, 290.20, 308.48, and 329.77 mu m were detected in the spectra of three planetary nebulae: NGC 6445, NGC6720, and NGC 6781. Excitation temperatures and column densities derived from these lines are in the range of 27-47 K and 2 x 10(10)-4 x 10(11) cm(-2), respectively. Conclusions. In PNe, the OH+ rotational line emission appears to be produced in the photodissociation region (PDR) in these objects. The emission of OH+ is observed only in PNe with hot central stars (T-eff > 100 000 K), suggesting that high-energy photons may play a role in OH+ formation and its line excitation in these objects, as seems to be the case for ultraluminous galaxies.
In this paper we give a progress report on the Herschel observations of planetary nebulae that are carried out as part of the MESS guaranteed time key program.
A large radio nebula around P Cygni Skinner, C. J.; Becker, R. H.; White, R. L. ...
Monthly notices of the Royal Astronomical Society,
05/1998, Letnik:
296, Številka:
3
Journal Article
Recenzirano
Odprti dostop
We present a large set of radio observations of the luminous blue variable P Cygni. These include two 6-cm images obtained with MERLIN which spatially resolve the 6-cm photosphere, monitoring ...observations obtained at Jodrell Bank every few days over a period of two months, and VLA observations obtained every month for seven years. This combination of data shows that the circumstellar environment of P Cyg is highly inhomogeneous, that there is a radio nebula extending to almost an arcminute from the star at 2 and 6 cm, and that the radio emission is variable on a time-scale no longer than one month, and probably as short as a few days. This short-time-scale variability is difficult to explain. We present a model for the radio emission with which we demonstrate that the star has probably been losing mass at a significant rate for at least a few thousand years, and that it has undergone at least two major outbursts of increased mass loss during the past two millenia.
A compact, variable radio nebula around P Cygni Skinner, C. J.; Exter, K. M.; Barlow, M. J. ...
Monthly notices of the Royal Astronomical Society,
06/1997, Letnik:
288, Številka:
1
Journal Article
Recenzirano
Odprti dostop
We present high spatial resolution images, at a wavelength of 6 cm, of the luminous blue variable star P Cygni. The images fully resolve the core of the stellar wind, and show that it is very clumpy. ...Two images were taken, separated in time by approximately a month, during which the structure in the wind has changed radically. The total flux observed has also changed significantly. We show that the clump sizes and electron densities are consistent with the radio variability being due to recombination of the ionized gas within the clumps, after key cooling lines become optically thin, causing the free-free emission to disappear. This is the first time that resolved radio images of a hot star wind have been obtained. It also represents important confirmation of a previous observation that thermal free-free wind emission can vary rapidly in a hot stellar wind.
Context. Recent studies have shown that stellar chromospheric activity, and its effect on convective energy transport in the envelope, is most likely the cause of significant radius and temperature ...discrepancies between theoretical evolution models and observations. Accurate mass, radius, and abundance determinations from solar-type binaries exhibiting various levels of activity are needed for a better insight into the structure and evolution of these stars. Aims. We aim to determine absolute dimensions and abundances for the solar-type detached eclipsing binary EF Aqr, and to perform a detailed comparison with results from recent stellar evolutionary models. Methods.uvby light curves and uvbyβ standard photometry were obtained with the Strömgren Automatic Telescope. The broadening function formalism was applied on spectra observed with HERMES at the Mercator telescope in La Palma, to obtain radial velocity curves. State-of-the-art methods were applied for the photometric and spectroscopic analyses. Results. Masses and radii with a precision of 0.6% and 1.0% respectively have been established for both components of EF Aqr. The active 0.956 M⊙ secondary shows star spots and strong Ca II H and K emission lines. The 1.224 M⊙ primary shows signs of activity as well, but at a lower level. An Fe/H abundance of 0.00 ± 0.10 is derived with similar abundances for Si, Ca, Sc, Ti, V, Cr, Co, and Ni. Solar calibrated evolutionary models such as Yonsei-Yale, Victoria-Regina and BaSTI isochrones and evolutionary tracks are unable to reproduce EF Aqr, especially for the secondary, which is 9% larger and 400 K cooler than predicted. Models adopting significantly lower mixing length parameters l/Hp remove these discrepancies, as seen in other solar type binaries. For the observed metallicity, Granada models with a mixing length of l/Hp = 1.30 (primary) and 1.05 (secondary) reproduce both components at a common age of 1.5 ± 0.6 Gyr. Conclusions. Observations of EF Aqr suggests that magnetic activity, and its effect on envelope convection, is likely to be the cause of discrepancies in both radius and temperature, which can be removed by adjusting the mixing length parameter of the models downwards.
Context. The standard stellar model atmosphere ignores the influence of external radiation. This assumption, while sufficient for most stars, fails for many short-period binaries. Aims. In setting up ...combined model atmospheres for close binaries, we want to constrain the parameters of both components, especially in the case of a hot primary component strongly influencing its cool secondary companion. This situation can be found after common envelope evolution (CEE). The status of both components today allows one to retrace the CEE itself. Methods. We used our stellar atmosphere code PHOENIX, which includes the effect of irradiation in its radiation transport equation, to investigate the close binary star UU Sge. We combined our calculated spectra of both components, weighted by their visible size, and adjusted the input parameters until reasonable agreement with observations is reached. Results. We derive a range of 80 000-85 000 K for the effective temperature of the primary $(T_{\mathrm{eff,\,p}})$ and give a rough estimate for the primary's abundances, particularly the nitrogen enrichment. The heated day-side of the secondary has an apparent “effective” or equilibrium temperature of 24 000-26 000 K, nearly independent of its intrinsic luminosity. It shows an enhancement in nitrogen and carbon. Conclusions. The evolution of the primary and secondary stars were strongly influenced by the other's presence. Radiation from the primary on the secondary's day-side is still an important factor in understanding the secondary's atmospheric structure.
Aims. We report the first detections of OH super(+) emission in planetary nebulae (PNe). Methods. As part of an imaging and spectroscopy survey of 11 PNe in the far-IR using the PACS and SPIRE ...instruments aboard the Herschel Space Observatory, we performed a line survey in these PNe over the entire spectral range between 51 mu m and 672 mu m to look for new detections. Results. The rotational emission lines of OH super(+) at 152.99, 290.20, 308.48, and 329.77 mu m were detected in the spectra of three planetary nebulae: NGC 6445, NGC 6720, and NGC 6781. Excitation temperatures and column densities derived from these lines are in the range of 27-47 K and 2 x 10 super(10)-4 x 10 super(11) cm super(-2), respectively. Conclusions. In PNe, the OH super(+) rotational line emission appears to be produced in the photodissociation region (PDR) in these objects. The emission of OH super(+) is observed only in PNe with hot central stars (T sub(eff)> 100 000 K), suggesting that high-energy photons may play a role in OH super(+) formation and its line excitation in these objects, as seems to be the case for ultraluminous galaxies.
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![Emission Lines of [Cl II] i...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/0004-637X/small "Emission Lines of [Cl II] in the Optical Spectra of Gaseous Nebulae")
