Estimating the Structure and Geometry of Winds from Luminous Blue Variables via Fitting the Continuum Energy Distributions

Guo, J.; Li, Y.

doi:10.1086/512228

Cited by 8 publications

(10 citation statements)

References 76 publications

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“…All these parameters, as well as wind clumping and line blanketing, affect the shape of the continuum, and the assumed values by Guo & Li (2007) are significantly different than the values derived in this paper. Our detailed fits to the line profiles require a much slower velocity law (β = 3) for the wind of AG Car than that determined by Guo & Li (2007). 7.3.…”

Section: Comparison With Previous Workcontrasting

confidence: 69%

ON THE NATURE OF THE PROTOTYPE LUMINOUS BLUE VARIABLE AG CARINAE. I. FUNDAMENTAL PARAMETERS DURING VISUAL MINIMUM PHASES AND CHANGES IN THE BOLOMETRIC LUMINOSITY DURING THE S-Dor CYCLE

Groh

Hillier

Damineli

et al. 2009

ApJ

139

181

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We present a detailed spectroscopic analysis of the luminous blue variable AG Carinae during the last two visual minimum phases of its S-Dor cycle (1985-1990 and 2000-2003). The analysis reveals an overabundance of He, N, and Na, and a depletion of H, C, and O, on the surface of AG Car, indicating the presence of CNO-processed material. Furthermore, the ratio N/O is higher on the stellar surface than in the nebula. We found that the minimum phases of AG Car are not equal to each other, since we derived a noticeable difference between the maximum effective temperature achieved during 1985-1990 (22, 800 K) and 2000-2001 (17, 000 K). Significant differences between the wind parameters in these two epochs were also noticed. While the wind terminal velocity was 300 km s −1 in 1985-1990, it was as low as 105 km s −1 in 2001. The mass-loss rate, however, was lower from 1985-1990 (1.5 × 10 −5 M ⊙ yr −1 ) than from 2000-2001 (3.7 × 10 −5 M ⊙ yr −1 ). We found that the wind of AG Car is significantly clumped (f ≃ 0.10 − 0.25) and that clumps must be formed deep in the wind. We derived a bolometric luminosity of 1.5 × 10 6 L ⊙ during both minimum phases which, contrary to the common assumption, decreases to 1.0 × 10 6 L ⊙ as the star moves towards maximum flux in the V band. Assuming that the decrease in the bolometric luminosity of AG Car is due to the energy used to expand the outer layers of the star (Lamers 1995), we found that the expanding layers contain roughly 0.6 − 2 M ⊙ . Such an amount of mass is an order of magnitude lower than the nebular mass around AG Car, but is comparable to the nebular mass found around lower-luminosity LBVs and to that of the Little Homunculus of Eta Car. If such a large amount of mass is indeed involved in the S Dor-type variability, we speculate that such instability could be a failed Giant Eruption, with several solar masses never becoming unbound from the star.

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Section: Comparison With Previous Workcontrasting

confidence: 69%

ON THE NATURE OF THE PROTOTYPE LUMINOUS BLUE VARIABLE AG CARINAE. I. FUNDAMENTAL PARAMETERS DURING VISUAL MINIMUM PHASES AND CHANGES IN THE BOLOMETRIC LUMINOSITY DURING THE S-Dor CYCLE

Groh

Hillier

Damineli

et al. 2009

ApJ

139

181

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“…Guo et al (2005) suggested that this may be due to a decrease of neutral hydrogen because of collisions in the dense wind, due to extra emission from the recombination of hydrogen, or due to the more extended atmospheres in which the velocity field changes with the radius and the lines of the Lyman series could be spread out. Guo & Li (2007) showed that the continuum energy distribution around the Balmer jump is sensitive to the wind velocity law. Second, the observed spectral energy distribution of LBVs in outburst may be a combination of two sources (the central star and the envelope).…”

Section: Discussionmentioning

confidence: 99%

Broad-band spectroscopy of the ongoing large eruption of the luminous blue variable R71

Mehner

Baade

Rivinius

et al. 2013

A&A

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Aims. The luminous blue variable (LBV) R71 is currently undergoing an eruption, which differs photometrically and spectroscopically from its last outburst in the 1970s. Valuable information on the physics of LBV eruptions can be gained by analyzing the spectral evolution during this eruption and by comparing R71's present appearance to its previous outburst and its quiescent state.Methods. An ongoing monitoring program with VLT/X-shooter will secure key spectral data ranging from visual to near- show H i and Fe ii P Cyg profiles, which were present during its last outburst in the 1970s and which are normally observed during LBV outbursts. Low-excitation forbidden emission lines and Fe i P Cyg-like profiles from a slowly expanding nebula became apparent in late 2012. These lines originate likely in the rarefied region above the pseudo-photosphere up to 13 AU from the star. Conclusions. The rise in R71's visual magnitude and the low apparent temperature of its pseudo-photosphere during the current eruption are unprecedented for this star. R71 most likely increased its bolometric luminosity by ΔM bol = 0.4-1.3 mag compared to its quiescent state. The very low temperature of its pseudo-photosphere implies a very high-mass loss rate on the order ofṀ R71,2012 ∼ 5 × 10 −4 M yr −1 compared toṀ quiescence ∼ 3 × 10 −7 M yr −1 . The apparent radius increased by a factor of 5 to about 500 R . No fastmoving material indicative of an explosion is observed. The changes in R71's photometry and spectrum are thus likely consequences of a tremendously increased wind density, which led to the formation of a pseudo-photosphere.

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“…In some objects in certain phases, however, β attains a significantly higher value, up to β∼ 4 (Najarro, Hillier & Stahl 1997; Groh et al 2009). In general, LBV stars have low β≲ 1 during optical minima, but the velocity law changes during eruptions (Guo & Li 2007). We now consider the effect of the variable β parameter on model spectrum.…”

Section: The Modelmentioning

confidence: 99%

Modelling the optical spectrum of Romano’s star★

Maryeva

Abolmasov

2011

Monthly Notices of the Royal Astronomical Society

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We consider the luminous blue variable (LBV) star V532 in M33, also known as Romano’s star, in two different spectral states: in the optical minimum of 2007/2008 and during a local brightening in 2005. Optical spectra of low and moderate resolution are modelled using the non‐local thermodynamic equilibrium model atmosphere code cmfgen. All the observed properties of the object in the minimum are well described by a late WN (nitrogen‐sequence Wolf‐Rayet) star model with a relatively high hydrogen abundance (H/He = 1.9), while the spectrum during the outburst corresponds to the spectral class WN11 and is similar to the spectrum of P Cyg. The atmosphere is enriched in nitrogen by about a factor of 6 in both states. Most of the heavy‐element abundances are consistent with the chemical composition of M33. Bolometric luminosity is shown to vary between the two states by a factor of ∼1.5. This makes V532 another example of an LBV that shows variations in its bolometric luminosity during an outburst.

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Estimating the Structure and Geometry of Winds from Luminous Blue Variables via Fitting the Continuum Energy Distributions

Cited by 8 publications

References 76 publications

ON THE NATURE OF THE PROTOTYPE LUMINOUS BLUE VARIABLE AG CARINAE. I. FUNDAMENTAL PARAMETERS DURING VISUAL MINIMUM PHASES AND CHANGES IN THE BOLOMETRIC LUMINOSITY DURING THE S-Dor CYCLE

ON THE NATURE OF THE PROTOTYPE LUMINOUS BLUE VARIABLE AG CARINAE. I. FUNDAMENTAL PARAMETERS DURING VISUAL MINIMUM PHASES AND CHANGES IN THE BOLOMETRIC LUMINOSITY DURING THE S-Dor CYCLE

Broad-band spectroscopy of the ongoing large eruption of the luminous blue variable R71

Modelling the optical spectrum of Romano’s star★

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