The massive eclipsing system HD 5980 in the Small Magellanic Cloud presented sudden ~1–3 mag eruptive events in 1993-1994, the nature of which is still unexplained. We recently showed that these ...brief eruptions occurred at the beginning of an extended high state of activity which is characterized by large emission-line intensities and that this high state is currently ending (Koenigsberger et al. 2010). Star A, the more massive member of the 19-day binary, is responsible for the spectacular spectral variations observed over the past 3 decades (see Figure 1). It has a He-enriched stellar wind and is over-luminous for its mass, implying an advanced evolutionary state (Koenigsberger et al. 1998). Data obtained over the past 3 decades show that Star A's wind speed slowed down as the system brightened. Also present in these data is a correlated increase in emission-line strength, visual and UV brigthness. The latter suggests that the high activity state in HD 5980 may be attributed to a bolometric luminosity increase, consistent with the results of Drissen et al. (2001). Hence, HD 5980 may be providing the important clues needed for understanding the behavior of other luminous blue variables and for understainding the evolutionary transition between massive O-type stars and Wolf-Rayet stars.
WR~21a was known as a massive spectroscopic binary composed of an O2.5 If*/WN6ha primary and an O3 V((f*))z secondary. Although a minimum value, the mass estimated for the primary placed it as one of ...the most massive stars found in our Galaxy. We report the discovery of photometric variations in the time series observations carried out by the Transiting Exoplanet Survey Satellite (TESS). These light variations are interpreted as formed by two main components: a sharp partial eclipse of the O3 secondary by the O2.5/WN6 star, and tidally excited oscillations. Based on the light minima a new ephemeris for the system is calculated. The system configuration is detached and the observed eclipse corresponds to the periastron passage. During the eclipse, the light curve shape suggests the presence of the heartbeat effect. The frequencies derived for the tidally excited oscillations are harmonics of the orbital period. Combining new and previously published radial velocity measurements, a new spectroscopic orbital solution is also obtained. Using the \textsc{phoebe} code we model the \textit{TESS} light curve and determine stellar radii of \(R_{\rm O2.5/WN6}=23.4\) R\(_\odot\) and \(R_{\rm O3}=14.3\) R\(_\odot\) and an orbital inclination \(i=62^\circ\!\!.2\pm0^\circ\!\!.9\). The latter combined with the spectroscopic minimum masses lead to absolute masses of \(M_{\rm O2.5/WN6}=93.2\) M\(_\odot\) and \(M_{\rm O3}=52.9\) M\(_\odot\), which establishes WR21a as belonging to the rare group of the very massive stars.
We present a comprehensive study of the massive binary system HM1~8, based on
multi-epoch high resolution spectroscopy, $V$-band photometry and archival
X-ray data. Spectra from the OWN Survey, a ...high resolution optical monitoring
of Southern O and WN stars, are used to analyse the spectral morphology and
perform quantitative spectroscopic analysis of both stellar components. The
primary and secondary components are classified as O4.5~IV(f) and O9.7~V,
respectively. From a radial-velocity (RV) study we derived a set of orbital
parameters for the system. We found an eccentric orbit ($e=0.14 \pm 0.01$) with
a period of $P = 5.87820 \pm 0.00008$~days. Through the simultaneous analysis
of the RVs and the $V$-band light curve we derived an orbital inclination of
$70.0^{\circ} \pm 2.0$ and stellar masses of
$M_a=33.6^{+1.4}_{-1.2}~\text{M}_{\sun}$ for the primary, and
$M_b=17.7^{+0.5}_{-0.7}~\text{M}_{\sun}$ for the secondary. The components show
projected rotational velocities $v_1\sin{i}=105 \pm 14~\text{km~s}^{-1}$ and
$v_2\sin{i}=82 \pm 15~\text{km~s}^{-1}$, respectively. A tidal evolution
analysis is also performed and found to be in agreement with the orbital
characteristics. Finally, the available X-ray observations show no evidence of
a colliding winds region, therefore the X-ray emission is attributed to stellar
winds.
We present HK spectra of three sources located in the N66 region of the Small Magellanic Cloud. The sources display prominent stellar Br Gamma and extended H2 emission, and exhibit infrared excesses ...at lambda > 2 micron. Based on their spectral features, and photometric spectral energy distributions, we suggest that these sources are massive young stellar objects (mYSOs). The findings are interpreted as evidence of on-going high mass star formation in N66.
We present a multiwavelength study of several star forming regions in the LMC and SMC. Broad and narrowband IR imaging in conjunction with cold molecular emission of CO lines and mid IR imaging by ...ISO are providing us the data to define the massive star content and formation processes in low metallicity environments (1/3 to 1/10 solar) for comparison with Galactic star forming regions. Our multiwavelength studies show a clear correlation between the 2.12 μm H^sub 2^, the 6.7 μm AIBs, and 230 GHz CO(2-1) emission as predicted by PDR models towards N66 in the SMC and 30 Doradus in the LMC. We have found IR embedded sources toward the peaks of the CO emission detected toward both HII regions. We find that the molecular gas that has not yet been photo dissociated by the UV radiation field of the O stars is in hot, dense clumps with very small filling factors. The distribution and morphology of the excited molecular gas in 30 Doradus as seen in the H^sub 2^ line is clumpy with numerous knots while that of the ionized gas in the 2.16 μm Brγ emission shows a filamentary structure. The 6.7 μm images show a good correlation to the Br γ emission as expected for warm gas. Towards N11 and N159 in the LMC we have also found several IR embedded sources associated to the presence of cold molecular gas. These are seen in the interfaces between the molecular material and the HII regions. Thus, either induced or trigered star formation occurs in these interfaces producing a PDR region.PUBLICATION ABSTRACT
APOGEE spectra offer \(\lesssim\)1 km s\(^{-1}\) precision in the measurement of stellar radial velocities (RVs). This holds even when multiple stars are captured in the same spectrum, as happens ...most commonly with double-lined spectroscopic binaries (SB2s), although random line of sight alignments of unrelated stars can also occur. We develop a code that autonomously identifies SB2s and higher order multiples in the APOGEE spectra, resulting in 7273 candidate SB2s, 813 SB3s, and 19 SB4s. We estimate the mass ratios of binaries, and for a subset of these systems with sufficient number of measurements we perform a complete orbital fit, confirming that most systems with period \(<\)10 days have circularized. Overall, we find a SB2 fraction (\(F_{SB2}\)) \(\sim\)3\% among main sequence dwarfs, and that there is not a significant trend in \(F_{SB2}\) with temperature of a star. We are also able to recover a higher \(F_{SB2}\) in sources with lower metallicity, however there are some observational biases. We also examine light curves from TESS to determine which of these spectroscopic binaries are also eclipsing. Such systems, particularly those that are also pre- and post-main sequence, are good candidates for a follow-up analysis to determine their masses and temperatures.
We present a detailed spectroscopic study of Herschel 36 A (H36A), the main stellar component of the massive multiple system Herschel 36 in the Hourglass Nebula, based on high-resolution optical ...spectra obtained along an 11 years span. The three stellar components present in the spectrum of H36A are separated by means of a spectral disentangling technique. Individual spectral classifications are improved, and high precision orbital solutions for the inner and the outer orbits are calculated. H36A is confirmed to be a hierarchical triple system composed of a close massive binary (Ab1+Ab2, O9.5 V+B0.7 V) in wide orbit around a third O-type star (Aa, O7.5 Vz). The inner-pair orbit is characterized by a period of 1.54157 +/- 0.00006 days, and semi-amplitudes of 181.2 +/- 0.7 and 295.4 +/- 1.7 km/s. The outer orbit has a period of 492.81 +/- 0.69 days, and semi-amplitudes of 62.0 +/- 0.6 and 42.4 +/- 0.8 km/s. Inner and outer orbits are not coplanar, having a relative inclination of at least 20 degrees. Dynamical minimum masses of 20.6 +/- 0.8 Msun, 18.7 +/- 1.1 Msun, and 11.5 +/- 1.1 Msun are derived for the Aa, Ab1, and Ab2 components, respectively, in reasonable agreement with the theoretical calibrations.
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![[ITAL]HUBBLE SPACE TELESCOP...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/0004-6256/small "[ITAL]HUBBLE SPACE TELESCOPE[/ITAL][ITAL]Hubble Space Telescope[/ITAL] NICMOS Detection of a Partially Embedded, Intermediate-Mass, Pre–Main-Sequence Population in the 30 Doradus Nebula")
