Cyclicities in the light variations of S Doradus stars

Groot, M. de; Sterken, C.; Genderen, A. M. van

doi:10.1051/0004-6361:20010960

Cited by 17 publications

(17 citation statements)

References 18 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…This estimate is in excellent agreement with values obtained from IR and radio observations,Ṁ IR = (2.2 ± 0.7) 10 −5 M yr −1 (Felli et al 1985) andṀ radio = (2.1 ± 0.4) 10 −5 M yr −1 (Scuderi et al 1998).…”

Section: Discussionsupporting

confidence: 89%

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

Маркова

Scuderi

Groot

et al. 2001

A&A

Self Cite

View full text Add to dashboard Cite

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.

show abstract

Section: Discussionsupporting

confidence: 89%

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

Маркова

Scuderi

Groot

et al. 2001

A&A

Self Cite

View full text Add to dashboard Cite

show abstract

“…De Groot et al (2001b) report a Fourier analysis of V -band observations of P Cygni covering the interval from 1982 to 2000 and showing a possible 4.5-year cyclic oscillation in the stellar brightness which they recognised as a short SD-phase. Yet, the scatter around the fitted sine curve suggests that this cycle is not quite unambiguous.…”

Section: Discussionmentioning

confidence: 99%

P Cygni in a short S Doradus phase. Spectroscopic and photometric evidences

Маркова

Morrison

Markov

2001

A&A

View full text Add to dashboard Cite

Abstract.We studied the long-term spectral and photometric behaviour of P Cygni over the 13.8 year interval from March 1985 to January 1999. The UBV photometry reveals a slow (∼7.4-year), low-amplitude (∼0.1 mag) variation in V in which the star becomes redder when it brightens and vice versa. It underwent a possible maximum in the winter of 1985 (between JD 2 446 000 and JD 2 446 200), a minimum in the winter of 1989 (between JD 2 447 500 and JD 2 447 700), a maximum in the fall of 1992 (between JD 2 448 800 and JD 2 449 000), and a minimum in the spring of 1996 (between JD 2 450 100 and JD 2 450 300) The properties of this variation are typical for weak-active S Dor variables in "short S Dor phase" (van Genderen 2001). Simultaneous spectroscopic observations show changes in the Hα equivalent width (corrected for the effect of the changing continuum) in positive correlation with the 7.4-year photometric oscillation in the V -band brightness. This result is interpreted as an indication that in P Cygni an increase in the stellar brightness, during the 7.4-year SD phase, is likely accompanied by an increase in the mass-loss rate. In this behaviour P Cygni is similar to S Dor and R71. From simple considerations, it is concluded that the 7.4-year SD cycle is probably a combination of an increasing radius/decreasing effective temperature and an expanding pseudo-photosphere.

show abstract

“… Increased mass‐loss : LBV's exhibit variability on a number of time‐scales (e.g. de Groot, Sterken & van Genderen 2001), and are known to go through eruptive phases where large amounts of stellar material are ejected into the surrounding interstellar medium (ISM). The primary star may be undergoing S Dor‐like fluctuations (van Genderen & Sterken 2007), which may reach a maximum around periastron with a shell‐ejection event (such an event was proposed by Davidson & Humphreys 1997, as an alternative to the binary eclipse model for explanation of the X‐ray minimum).…”

Section: The X‐ray Minimummentioning

confidence: 99%

3D modelling of the colliding winds in η Carinae - evidence for radiative inhibition

Parkin

Pittard

Corcoran

et al. 2009

Monthly Notices of the Royal Astronomical Society

124

207

View full text Add to dashboard Cite

The X‐ray emission from the supermassive star η Car is simulated using a 3D model of the wind–wind collision. In the model the intrinsic X‐ray emission is spatially extended and energy dependent. Absorption due to the unshocked stellar winds and the cooled post‐shock material from the primary LBV star is calculated as the intrinsic emission is ray traced along multiple sightlines through the 3D spiral structure of the circumstellar environment. The observable emission is then compared to available X‐ray data, including the light curve observed by the Rossi X‐ray Timing Explorer (RXTE) and spectra observed by XMM–Newton. The orientation and eccentricity of the orbit are explored, as are the wind parameters of the stars and the nature and physics of their close approach. Our modelling supports a viewing angle with an inclination of ≃42°, consistent with the polar axis of the Homunculus nebula, and the projection of the observer's line of sight on to the orbital plane has an angle of ≃0°–30° in the prograde direction on the apastron side of the semimajor axis. However, there are significant discrepancies between the observed and model light curves and spectra through the X‐ray minimum. In particular, the hard flux in our synthetic spectra is an order of magnitude greater than observed. This suggests that the hard X‐ray emission near the apex of the wind–wind collision region (WCR) ‘switches off’ from periastron until two months afterwards. Further calculations reveal that radiative inhibition significantly reduces the pre‐shock velocity of the companion wind. As a consequence the hard X‐ray emission is quenched, but it is unclear whether the long duration of the minimum is due solely to this mechanism alone. For instance, it is possible that the collapse of the WCR on to the surface of the companion star, which would be aided by significant inhibition of the companion wind, could cause an extended minimum as the companion wind struggles to re‐establish itself as the stars recede. For orbital eccentricities, e≲ 0.95, radiative braking prevents a wind collision with the companion star's surface. Models incorporating a collapse/disruption of the WCR and/or reduced pre‐shock companion wind velocities bring the predicted emission and the observations into much better agreement.

show abstract

Cyclicities in the light variations of S Doradus stars

Cited by 17 publications

References 18 publications

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

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

P Cygni in a short S Doradus phase. Spectroscopic and photometric evidences

3D modelling of the colliding winds in η Carinae - evidence for radiative inhibition

Contact Info

Product

Resources

About