Abstract
ABSTRACT Mid-infrared photometry of the Wolf-Rayet star HD 38030 in the Large Magellanic Cloud from the NEOWISE-R mission show it to have undergone a dust-formation episode in 2018 and the dust to have cooled in 2019–20. New spectroscopy with the MagE spectrograph on the Magellan I Baade Telescope in 2019 and 2020 show absorption lines attributable to a companion of type near O9.7III-IV. We found a significant shift in the radial velocity of the C iv λλ5801–12 blend compared with the RVs measured in 1984 and 1993. The results combine to suggest that HD 38030 is a colliding-wind binary having short-lived dust formation episodes, like the Galactic systems WR 140 and WR 19, but at intervals in excess of 20 yr.
Highlights
It has long been known from infrared (IR) observations (Allen, Swings & Harvey 1972) that some Galactic WC-type Wolf-Rayet (WR) stars make carbon dust in their winds
It is evident that there is a real velocity shift, 77±12 km s−1, between the two datasets. Assuming that this shift is not caused by variations in the shape of the C emission-line profile, this supports the notion that the absorption-line spectrum forms in a physical companion to the WC4 star and the HD 38030 is a colliding wind binary (CWB)
Our new spectroscopy shows a well developed absorption-line spectrum pointing to the presence of a companion to the WC4 star, which we classified as O9.7 with a tentative luminosity class of III or IV
Summary
It has long been known from infrared (IR) observations (Allen, Swings & Harvey 1972) that some Galactic WC-type Wolf-Rayet (WR) stars make carbon dust in their winds Most of these WR dust makers do so persistently and are of spectral sub-types WC8–9 (Williams, van der Hucht & Thé 1987) but a few WR dust makers are of earlier subtypes and make their dust in brief, but regular, episodes at intervals of the order of a decade. The latter stars have been shown to be members of massive binary systems having highly elliptical orbits wherein the episodes of dust formation coincide with periastron passage, e.g. WR 140 (Williams et al 1990) and WR 19 (Williams et al 2009a). Amongst the WC stars found to show variable dust emission (Williams 2019) was HD 380301 in the LMC: in 2018, after some years of apparent constancy in the IR, its W1 (3.4-μm) and W2 (4.6-μm) fluxes brightened by 1–2 magnitudes and its W1 − W2 colour became more characteristic of emission by heated dust
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