Over the past 40 years, the massive LBV/WR system HD 5980 in the Small Magellanic Cloud has undergone a long-term S Doradus type variability cycle and two brief and violent eruptions in 1993 and ...1994. In this paper we analyze a collection of UV and optical spectra obtained between 1979 and 2009 and perform CMFGEN model fits to spectra of 1994, 2000, 2002 and 2009. The results are as follows: a) The long term S Dor-type variability is associated with changes of the hydrostatic radius; b) The 1994 eruption involved changes in its bolometric luminosity and wind structure; c) the emission-line strength, the wind velocity and the continuum luminosity underwent correlated variations in the sense that a decreasing V\(_\infty\) is associated with increasing emission line and continuum levels; and d) The spectrum of the third star in the system ({\it Star C}) is well-fit by a T\(_{eff}\)=32 K model atmosphere with SMC chemical abundances. For all epochs, the wind of the erupting star is optically thick at the sonic point and is thus driven mainly by the continuum opacity. We speculate that the wind switches between two stable regimes driven by the "hot" (during the eruption) and the "cool" (post-eruption) iron opacity bumps as defined by Lamers & Nugis (2002) and Gr\"afener and Hamann (2008), and thus the wind may undergo a bi-stability jump of a different nature from that which occurs in OB-stars.
With new data from the Galactic O-Star Spectroscopic Survey, we confirm and expand the ONn category of late-O, nitrogen-enriched (N), rapidly rotating (n) giants. In particular, we have discovered ...two "clones" (HD 102415 and HD 117490) of one of the most rapidly rotating O stars previously known (HD 191423, "Howarth's Star"). We compare the locations of these objects in the theoretical HR Diagram to those of slowly rotating ON dwarfs and supergiants. All ON giants known to date are rapid rotators, whereas no ON dwarf or supergiant is; but all ON stars are small fractions of their respective spectral-type/luminosity-class/rotational subcategories. The ONn giants, displaying both substantial processed material and high rotation at an intermediate evolutionary stage, may provide significant information about the development of those properties. They may have preserved high initial rotational velocities or been spun up by TAMS core contraction; but alternatively and perhaps more likely, they may be products of binary mass transfer. At least some of them are also runaway stars.
New Astron. 7 (2002) 511-520 We present the discovery of OB type absorption lines superimposed to the
emission line spectrum and the first double-lined orbital elements for the
massive Wolf-Rayet ...binary HDE 318016 (=WR 98), a spectroscopic binary in a
circular orbit with a period of 47.825 days. The semiamplitudes of the orbital
motion of the emission lines differ from line to line, indicating mass ratios
between 1 and 1.7 for M_WR/M_OB.
We present the discovery of OB type absorption lines superimposed to the
emission line spectrum, and the first double-lined orbital elements for the
massive Wolf-Rayet binary HDE 318016 (=WR 98), a ...spectroscopic binary in a
circular orbit with a period of 47.825 days. The semiamplitudes of the orbital
motion of the emission lines differ from line to line, indicating mass ratios
between 1 and 1.7 for MWR/MOB.
On the basis of an extensive new spectroscopic survey of Galactic O stars, we introduce the Ofc category, which consists of normal spectra with C III \lambda\lambda4647-4650-4652 emission lines of ...comparable intensity to those of the Of defining lines N III \lambda\lambda4634-4640-4642. The former feature is strongly peaked to spectral type O5, at all luminosity classes, but preferentially in some associations or clusters and not others. The relationships of this phenomenon to the selective C III \lambda5696 emission throughout the normal Of domain, and to the peculiar, variable Of?p category, for which strong C III \lambda\lambda4647-4650-4652 emission is a defining characteristic, are discussed. Magnetic fields have recently been detected on two members of the latter category. We also present two new extreme Of?p stars, NGC 1624-2 and CPD -28^{\circ}2561, bringing the number known in the Galaxy to five. Modeling of the behavior of these spectral features can be expected to better define the physical parameters of both normal and peculiar objects, as well as the atomic physics involved.
In this poster we show our preliminary analysis of DIBs (Diffuse Interstellar Bands) and other interstellar absorption lines with the purpose of understanding their origin and their relationship with ...extinction. We use the biggest Galactic O-star blue-violet spectroscopic sample ever (GOSSS, see contribution by Maíz Apellániz at this meeting). This sample allows a new insight on this topic because of the adequacy of O-star spectra, the sample number (700 and increasing, 400 used here), and their distribution in the MW disk. We confirm the high correlation coefficients between different DIBs and E(B - V), though the detailed behavior of each case shows small differences. We also detect a moderately low correlation coefficient between Ca II {\lambda}3934 (Ca K) and E(B - V) with a peculiar spatial distribution that we ascribe to the relationship between line saturation and velocity profiles for Ca II {\lambda}3934.
The Galactic O-Star Spectroscopic Survey (GOSSS) is a project that is observing all known Galactic O stars with B < 13 (~2000 objects) in the blue-violet part of the spectrum with R~2500. It also ...includes two companion surveys (a spectroscopic one at R~1500 and a high resolution imaging one). It is based on v2.0 of the Galactic O star catalog (v1, Maíz Apellániz et al. 2004; v2, Sota et al. 2008). We have completed the first part of the main project. Here we present results on the first 400 objects of the sample.
We report optical observations of the Luminous Blue Variable (LBV) HR Carinae which show that the star has reached a visual minimum phase in 2009. More importantly, we detected absorptions due to Si ...IV 4088-4116 Angstroms. To match their observed line profiles from 2009 May, a high rotational velocity of vrot=150 +- 20 km/s is needed (assuming an inclination angle of 30 degrees), implying that HR Car rotates at ~0.88 +- 0.2 of its critical velocity for break-up (vcrit). Our results suggest that fast rotation is typical in all strong-variable, bona-fide galactic LBVs, which present S Dor-type variability. Strong-variable LBVs are located in a well-defined region of the HR diagram during visual minimum (the "LBV minimum instability strip"). We suggest this region corresponds to where vcrit is reached. To the left of this strip, a forbidden zone with vrot/vcrit>1 is present, explaining why no LBVs are detected in this zone. Since dormant/ex LBVs like P Cygni and HD 168625 have low vrot, we propose that LBVs can be separated in two groups: fast-rotating, strong-variable stars showing S-Dor cycles (such as AG Car and HR Car) and slow-rotating stars with much less variability (such as P Cygni and HD 168625). We speculate that SN progenitors which had S-Dor cycles before exploding (such as in SN 2001ig, SN 2003bg, and SN 2005gj) could have been fast rotators. We suggest that the potential difficulty of fast-rotating Galactic LBVs to lose angular momentum is an additional evidence that such stars could explode during the LBV phase.
We present the analysis of high-resolution optical spectroscopic observations of the zero-age main-sequence O star Herschel 36 spanning six years. This star is definitely a multiple system, with at ...least three components detected in its spectrum. Based on our radial-velocity (RV) study, we propose a picture of a close massive binary and a more distant companion, most probably in wide orbit about each other. The orbital solution for the binary, whose components we identify as O9 V and B0.5 V, is characterized by a period of 1.5415 +/- 0.0006 days. With a spectral type O7.5 V, the third body is the most luminous component of the system and also presents RV variations with a period close to 498 days. Some possible hypotheses to explain the variability are briefly addressed and further observations are suggested.
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