ABSTRACT
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 phoebe code we model the TESS light curve and determine stellar radii of RO2.5/WN6 = 23.4 R⊙ and RO3 = 14.3 R⊙ and an orbital inclination i = 62${_{.}^{\circ}}$2 ± 0${_{.}^{\circ}}$9. The latter combined with the spectroscopic minimum masses lead to absolute masses of MO2.5/WN6 = 93.2 M⊙ and MO3 = 52.9 M⊙, which establishes WR 21a as belonging to the rare group of the very massive stars.
Abstract
We report on a chemo-dynamical analysis of SPLUS J142445.34−254247.1 (SPLUS J1424−2542), an extremely metal-poor halo star enhanced in elements formed by the rapid neutron-capture process (
...r
-process). This star was first selected as a metal-poor candidate from its narrowband 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 the 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
log
ϵ
(
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 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
M
⊙
, and the heavy-element (
Z
≥ 38) abundance pattern can be reproduced by the yields from a neutron star merger (1.66
M
⊙
and 1.27
M
⊙
) 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.
Photometric CCD UB VIC 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: and . 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 0.19 kpc and 2.49 0.09 kpc are derived for SAI 113 and van Genderen 1, respectively, with variable reddenings 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.
ABSTRACT On the basis of the Galactic O Star Spectroscopic Survey (GOSSS), we present a detailed systematic investigation of the O Vz stars. The currently used spectral classification criteria are ...rediscussed, and the Vz phenomenon is recalibrated through the addition of a quantitative criterion based on the equivalent widths of the He iλ4471, He iiλ4542, and He iiλ4686 spectral lines. The GOSSS O Vz and O V populations resulting from the newly adopted spectral classification criteria are comparatively analyzed. The locations of the O Vz stars are probed, showing a concentration of the most extreme cases toward the youngest star-forming regions. The occurrence of the Vz spectral peculiarity in a solar-metallicity environment, as predicted by the fastwind code, is also investigated, confirming the importance of taking into account several processes for the correct interpretation of the phenomenon.
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 H-R 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 these properties. They may have preserved high initial rotational velocities or may have been spun up by terminal-age main-sequence core contraction; alternatively, and perhaps more likely, they may be products of binary mass transfer. At least some of them are also runaway stars.
ABSTRACT
Using the Las Cumbres Observatory Global Telescope Network (LCOGT), we have obtained multi-epoch photometry of the young cluster Mon R2. We have monitored over 6000 sources with i-band ...between 13 and 23 mag within a 26 × 26 arcmin2 field of view. For each star, we collected ∼1500 photometric points covering a temporal window of 23 d. Based on these data, we have measured rotation-modulated of 136 stars and identified around 90 additional variables, including 14 eclipsing binary candidates. Moreover, we found 298 other variables with photometric high-scatter. In addition, we have obtained r-band and Hα narrow-band photometry of the cluster with LCOGT and low-resolution optical spectroscopy of 229 stars with GMOS-Gemini. We used the Gaia data from the periodic stars and objects with Hα or IR-excesses, which are mostly low-mass pre-main sequence stars (<1 M⊙) in the cluster to estimate the distance (825 ± 51 pc) and the mean proper motions (μαcos(δ) = −2.75 mas yr−1 and μδ = 1.15 mas yr−1) of its members. This allows us to use the Gaia data to identify additional Mon R2 member candidates. We also used Pan-STARRS photometry from our LCOGT sources to construct a more precise H-R diagram, from which we estimate the mean age of the cluster and identify other possible members including eleven spectroscopy brown dwarf with M7 to M9 GMOS spectral types. Finally, we combined our membership lists with Spitzer infrared photometry to investigate the incidence of stars with discs and the effect these have on stellar rotation.
The paradigmatic luminous blue variable R127 in the Large Magellanic Cloud has been found in the intermediate, peculiar early-B state, and substantially fainter in visual light, signaling the final ...decline from its major outburst that began between 1978 and 1980. This transformation was detected in 2008 January, but archival data show that it began between early 2005 and early 2007. In fact, significant changes from the maximum, peculiar A-type spectrum, which was maintained from 1986 through 1998, had already begun the following year, coinciding with a steep drop in visual light. We show detailed correspondences between the spectrum and light, in which the decline mimics the rise. Moreover, these trends are not monotonic but are characterized by multiple spikes and dips, which may provide constraints on the unknown outburst mechanism. Intensive photometric and spectroscopic monitoring of R127 should now resume, to follow the decline presumably back to the quiescent Ofpe/WN9 state, in order to fully document the remainder of this unique observational opportunity.
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