The variable mass loss of the peculiar supergiant P Cygni

Israelian, G.; Groot, M. de; Parker, J. W.; Sterken, C.

doi:10.1093/mnras/283.1.119

Cited by 10 publications

(22 citation statements)

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“…By chance, our photographic observations partly overlap the UV observations studied by Israelian et al (1996). Combining the velocity measurements obtained for DACs in the optical (present study) with measurements derived for DACs in the UV we found that the two datasets agreed quite well in a sense that they defined a smooth curve of gradually increasing velocity (Fig.…”

Section: Dac-induced Variabilitysupporting

confidence: 77%

“…In view of this apparent ubiquity of the phenomenon the result reported by Stahl et al (1994) was really a surprise: no DAC was found in any of the CCD spectra taken over the years 1990 to 1992. Motivated by this finding Israelian et al (1996) studied the variability of UV metal lines and found that these lines still showed DACs in 1990. To bring all these results into line one must assume, either that the majority of DACs detected in the optical by previous investigators were not real but due to unrecognised photographic noise, or that the activity of the mechanism that causes the appearance of DACs in the optical has changed and that, as a result, the components disappeared.…”

Section: Introductionmentioning

confidence: 97%

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New aspects of line-profile variability in P Cygni's optical spectrum

Маркова

2000

Astron. Astrophys. Suppl. Ser.

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Abstract. High-resolution photographic spectra as well as high S/N ratio CCD spectral observations of P Cygni are analyzed in terms of line-profile variability (lpv). Four different kinds of lpv are established: systematic variability in the absorption troughs of low and intermediate excitation lines due to propagating Discrete Absorption Components (DACs); "swaying" variability consisting of continuous modulations in velocity and intensity of the absorption cores and emission peaks of lines of intermediate and high excitation; red-emission-wing variability due to travelling "bumps", and long-term (LT) variability in HI and HeI lines of relatively large optical depth. DAC propagation is a slow variation of P Cygni's stellar wind. The components probably originate from large-scale, high-density (low-excitation) perturbation(s) which develop in a relatively outer part of the wind (V ≥ 0.41V inf ) but appear to be maintained, in some indirect way, by photospheric processes. The geometry of the structures is not yet clear but they could be either spherically symmetric or curved, like kinks.The "swaying" variability manifests itself by modulations in position and intensity of the absorption cores and emission peaks of almost all lines in the optical. Simultaneous variations in emission and absorption linestrength were also observed. The modulations are at least partially due to variations in the number density which affect all layers of the supersonic wind starting at its base up to layers where the Hff line forms (0.18 ≤ V ≤ 0.95V inf ). The phenomenon appears to be stable over many years, though on a variable time-scale. Suggestive evidence for a close relationship between the modulations and changes in the stellar brightness and temperature was found, indicating that the "swaying" variability is more likely coupled to processes in the photosphere. Non-radial pulsations (NRPs) either of g-mode or of s-mode oscillations are a possible cause for this variability.The LT variability makes up a very slow pattern of variation in both the velocity of the absorption cores and the intensity of the emission peaks of the stronger HI and HeI lines. This variability is found only in the outer part of the wind (V ≤ 0.82V inf ). The nature of the LT variation is not known at present.The red-emission-wing variability is localized in the high-velocity part of the emission lobes of P Cygni-type profiles, +90 ≤ V ≤ +230/250 km s −1 . This variability is presumably caused by outward propagating "bumps", but its exact nature is still unknown.No indication for any clear relation between different kinds of lpv was found. Even when the variations operate in one and the same region of the wind (in velocity space) it is not obvious whether and how they interact. Stellar rotation does not seem to play a fundamental role in setting the time-scale of either the DAC-induced variability or the LT variability. The relationship between the "swaying" variability and the rotation is still not clear but it is possible that this variability is rotatio...

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Section: Dac-induced Variabilitysupporting

confidence: 77%

Section: Introductionmentioning

confidence: 97%

New aspects of line-profile variability in P Cygni's optical spectrum

Маркова

2000

Astron. Astrophys. Suppl. Ser.

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“…These 100 d-type cycles show a highly variable duration as well: between 60 d and 130 d, but this is not abnormal. Israelian et al (1996) suggested a correlation between the visual changes to a maximum (using part of the photometry presented here) and the ejection of recurrent shells deduced from the so-called discrete absorption components (DACs) as seen in IUE spectra. They estimated the frequency of the shells between 150 d and 250 d. However, this could well be an upper limit since the IUE observations show large gaps in time series.…”

Section: Discussionmentioning

confidence: 71%

Cyclicities in the light variations of S Doradus stars

Groot

Sterken²,

Genderen

2001

A&A

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Abstract. On the basis of new photometric observations and archived data published since 1907, we discuss the light variations of P Cygni. We conclude that there are α Cygni-type microvariations with a stable (pulsation) quasi-period of 17.3 days. There are also longer cycles of variation with P ∼ 100 d, so-called 100 d-type microvariations, and with P ∼ 1500-1600 d, a short S Dor-type phase.

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“…Markova 1993Markova , 2000Scuderi et al 1994;Stahl et al 1994a) and UV (e.g. Lamers et al 1985;Israelian et al 1996) wavelengths, radio-flux variability (van den Oord et al 1985;Skinner et al 1997), and polarisation variability (Hayes 1985;Taylor et al 1991). In addition, the star has also shown photometric variability on time-scales ranging from 40 to several hundred days (Percy et al 1988;de Groot 1990;Percy et al 1996).…”

Section: Introductionmentioning

confidence: 99%

“…Several studies have attempted to establish a connection between the variations for which the star's atmosphere is thought to be responsible and the corresponding variations in the wind but, in general, the results have been contradictory. For example, a relationship between brightness variations and changes in line profiles due to the recurrent appearance of Discrete Absorption Components (DACs) was suggested by Israelian et al (1996). De Groot (1990) and Percy et al (1996) suggested the existence of a correlation between the Hα emission-flux variability and variations in the V -band.…”

Section: Introductionmentioning

confidence: 99%

Simultaneous H$\mathsf{\alpha}$ and photometric observations of P Cygni

Маркова

Scuderi

Groot

et al. 2001

A&A

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Abstract. For the first time an extensive set of (quasi-) simultaneous photometric (UBV ) and spectroscopic (Hα line profiles) observations of P Cygni, covering a period from May, 1990 to June, 1994 was analyzed in terms of time variability. It is found that the Hα equivalent width (EW ) exhibits two different patterns of variability: a slower one, called Long-Term (LT) variability, with an amplitude of about 30Å and a characteristic duration of about 600 days and a faster one, called Short-Term (ST) variability, with an amplitude up to 10Å and duration of 40 to 60 days. Suggestive evidence for EW variation on a longer time scale (about few years) also exists. The variations in the Hα luminosity are not solely due to changes in the underlying continuum but also reflect variations in the physical properties of the wind. We find, in terms of a simplified spherically-symmetric wind model, that the LT variation of the line can be successfully explained in terms of a 26% alteration of the mass-loss rate, possibly accompanied by variations in the velocity field. From the analysis of the photometric behaviour of the star we find evidence for a very slow variation in the stellar brightness with an amplitude of about 0.13 mag and a duration of about 2600 days, i.e. about 7 years. During this variation, i.e. when the star brightens, the effective temperature decreases (by about 10%) and the radius increases (by about 7%). The properties of this Very Long Term (VLT) variation suggest that P Cygni has probably experienced a normal S Dor-type variation with a minimum phase around 1988 and a maximum phase in 1992. Some hints for a positive correlation between mass loss variations and changes in the stellar radius, due to the normal SD variability, do exist implying that the behaviour of P Cygni is more likely similar to that of R71 and S Dor but different from e.g. AG Car, R127 and HD 160529. Superimposed on the VLT component in the photometric variability of P Cygni, we observe ST brightness variations with an amplitude between 0.1 and 0.2 mag which appears to recur on a time scale of three to four months. The colour behaviour of these microvariations, at least of those which appear near the maximum phase of the VLT variation, is redder in B − V and bluer in U − B when the star brightens in V . The properties of this ST photometric variability are similar to the properties of the so-called "100 d-type micro-variations", recognized in other LBVs by van Genderen et al. (1997a,b). Based on time-scale evidences we suggest that the microvariabilities observed are rather due to "relaxation oscillations" (Stothers & Chin 1995) than to strange-mode oscillations in the stellar interior. Evidence for a close relationship between ST variations in Hα and changes in the stellar brightness and temperature is found. From other results about P Cygni's spectral variations (Markova 2000a), we conclude that the ST variability of the wind is most likely connected with processes in the stellar photosphere.

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The variable mass loss of the peculiar supergiant P Cygni

Cited by 10 publications

References 0 publications

New aspects of line-profile variability in P Cygni's optical spectrum

New aspects of line-profile variability in P Cygni's optical spectrum

Cyclicities in the light variations of S Doradus stars

Simultaneous H$\mathsf{\alpha}$ and photometric observations of P Cygni

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