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.
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.
Pristine_183.6849+04.8619 (P1836849) is an extremely metal-poor (Fe/H\(=-3.3\pm0.1\)) star on a prograde orbit confined to the Galactic disk. Such stars are rare and may have their origins in ...protogalactic fragments that formed the early Milky Way, in low mass satellites accreted later, or forming in situ in the Galactic plane. Here we present a chemo-dynamical analysis of the spectral features between \(3700-11000\)Å from a high-resolution spectrum taken during Science Verification of the new Gemini High-resolution Optical SpecTrograph (GHOST). Spectral features for many chemical elements are analysed (Mg, Al, Si, Ca, Sc, Ti, Cr, Mn, Fe, Ni), and valuable upper limits are determined for others (C, Na, Sr, Ba). This main sequence star exhibits several rare chemical signatures, including (i) extremely low metallicity for a star in the Galactic disk, (ii) very low abundances of the light \(\alpha\)-elements (Na, Mg, Si) compared to other metal-poor stars, and (iii) unusually large abundances of Cr and Mn, where Cr, Mn/Fe\(_{\rm NLTE}>+0.5\). A comparison to theoretical yields from supernova models suggests that two low mass Population III objects (one 10 M\(_\odot\) supernova and one 17 M\(_\odot\) hypernova) can reproduce the abundance pattern well (reduced \(\chi^2<1\)). When this star is compared to other extremely metal-poor stars on quasi-circular, prograde planar orbits, differences in both chemistry and kinematics imply there is little evidence for a common origin. The unique chemistry of P1836849 is discussed in terms of the earliest stages in the formation of the Milky Way.
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 report on the chemo-dynamical analysis of SPLUS J142445.34-254247.1, an extremely metal-poor halo star enhanced in elements formed by the rapid neutron-capture process. This star was first ...selected as a metal-poor candidate from its narrow-band S-PLUS photometry and followed up spectroscopically in medium-resolution with Gemini South/GMOS, which confirmed its low-metallicity status. High-resolution spectroscopy was gathered with GHOST at Gemini South, allowing for the determination of chemical abundances for 36 elements, from carbon to thorium. At Fe/H=-3.39, SPLUS J1424-2542 is one of the lowest metallicity stars with measured Th and has the highest logeps(Th/Eu) observed to date, making it part of the "actinide-boost" category of r-process enhanced stars. The analysis presented here suggests that the gas cloud from which SPLUS J1424-2542 was formed must have been enriched by at least two progenitor populations. The light-element (Z<=30) abundance pattern is consistent with the yields from a supernova explosion of metal-free stars with 11.3-13.4 Msun, and the heavy-element (Z>=38) abundance pattern can be reproduced by the yields from a neutron star merger (1.66Msun and 1.27Msun) event. A kinematical analysis also reveals that SPLUS J1424-2542 is a low-mass, old halo star with a likely in-situ origin, not associated with any known early merger events in the Milky Way.
Context. At least 492 central stars of Galactic planetary nebulae (CSPNs) have been assigned spectral types. Since many CSPNs are faint, these classification efforts are frequently made at low ...spectral resolution. However, the stellar Balmer absorption lines are contaminated with nebular emission; therefore in many cases a low-resolution spectrum does not enable the determination of the H abundance in the CSPN photosphere. Whether or not the photosphere is H deficient is arguably the most important fact we should expect to extract from the CSPN spectrum, and should be the basis for an adequate spectral classification system. Aims. Our purpose is to provide accurate spectral classifications and contribute to the knowledge of central stars of planetary nebulae and stellar evolution. Methods. We have obtained and studied higher quality spectra of CSPNs described in the literature as weak emission-line star (WELS). We provide descriptions of 19 CSPN spectra. These stars had been previously classified at low spectral resolution. We used medium-resolution spectra taken with the Gemini Multi-Object Spectrograph (GMOS). We provide spectral types in the Morgan-Keenan (MK) system whenever possible. Results. Twelve stars in our sample appear to have normal H rich photospheric abundances, and five stars remain unclassified. The rest (two) are most probably H deficient. Of all central stars described by other authors as WELS, we find that at least 26% of them are, in fact, H rich O stars, and at least 3% are H deficient. This supports the suggestion that the denomination WELS should not be taken as a spectral type, because, as a WELS based on low-resolution spectra, it cannot provide enough information about the photospheric H abundance.
Context. There are more than 3000 confirmed and probable known Galactic planetary nebulae, but central star spectroscopic information is available for only 13% of them. Aims. We undertook a ...spectroscopic survey of central stars of PNe to identify their spectral types. Methods. We performed spectroscopic observations, at low resolution, with the 2-m telescope at CASLEO, Argentina. Results. We present the spectra of 46 central stars of PNe, most of them are OB-type and emission-line stars.
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.
Photometric CCD {\it UBVI}\(_C\) photometry obtained for 4860 stars surrounding the embedded southern cluster SAI~113 (Skiff~8) is used to examine the reddening in the field and derive the distance ...to the cluster and nearby van~Genderen~1. Spectroscopic color excesses for bright cluster stars, photometric reddenings for A3 dwarfs, and dereddening of cluster stars imply that the reddening and extinction laws match results derived for other young clusters in Carina: E\(_{U-B}/\)E\(_{B-V} \simeq 0.64\) and \(R_V \simeq 4\). SAI~113 displays features that may be linked to a history of dynamical interactions among member stars: possible circumstellar reddening and rapid rotation of late B-type members, ringlike features in star density, and a compact core with most stars distributed randomly across the field. The group van~Genderen~1 resembles a stellar asterism, with potential members distributed randomly across the field. Distances of \(3.90 \pm0.19\) kpc and \(2.49 \pm0.09\) kpc are derived for SAI~113 and van~Genderen~1, respectively, with variable reddenings E\(_{B-V}\) ranging from 0.84 to 1.29 and 0.23 to 1.28. The SRC variables CK~Car and EV~Car may be outlying members of van~Genderen~1, thereby of use for calibrating the period-luminosity relation for pulsating M supergiants. More importantly, the anomalous reddening and extinction evident in Carina and nearby regions of the Galactic plane in the fourth quadrant impact the mapping of spiral structure from young open clusters. The distribution of spiral arms in the fourth quadrant may be significantly different from how it is often portrayed.
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