The SALT HRS spectrograph: final design, instrument capabilities, and operational modes

Bramall, David; Sharples, R. M.; Tyas, Luke; Schmoll, J.; Clark, Paul; Luke, Peter; Looker, N.; Dipper, N. A.; Ryan, Sean G.; Buckley, D.; Brink, Janus D.; Barnes, Stuart

doi:10.1117/12.856382

Cited by 56 publications

(34 citation statements)

References 5 publications

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“…Since HD 42659 is the only roAp star known to be in a spectroscopic binary system (Hartmann & Hatzes 2015), it provides us with the opportunity to test whether the binary companion affects the pulsations in the Ap star. To that end, we obtained 27 spectra with the High Resolution Spectrograph (HRS; Bramall et al 2010;Crause et al 2014) mounted on the Southern African Large Telescope (SALT; Buckley et al 2006). Observations were taken in High Resolution (HR) mode, R ≃ 65 000, with an integration time of 158 s. The signal-to-noise ratio varied between about 100 and 150 in the central region of the spectrum, dependent on observing conditions.…”

Section: Spectroscopymentioning

confidence: 99%

HD 42659: the only known roAp star in a spectroscopic binary observed with B photometry, TESS, and SALT

Holdsworth

Saio

Kurtz

2019

Monthly Notices of the Royal Astronomical Society

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We present a multi-instrument analysis of the rapidly oscillating Ap (roAp) star HD 42659. We have obtained B photometric data for this star and use these data, in conjunction with TESS observations, to analyse the high-frequency pulsation in detail. We find a triplet which is split by the rotation frequency of the star (ν rot = 0.3756 d −1 ; P rot = 2.66 d) and present both distorted dipole and distorted quadrupole mode models. We show that the pulsation frequency, 150.9898 d −1 (P puls = 9.54 min) is greater than the acoustic cutoff frequency. We utilise 27 high-resolution (R ≃ 65 000), high signal-to-noise (∼ 120) spectra to provide new orbital parameters for this, the only known roAp star to be in a short period binary (P orb = 93.266 d). We find the system to be more eccentric than previously thought, with e = 0.317, and suggest the companion is a mid-F to early-K star. We find no significant trend in the average pulsation mode amplitude with time, as measured by TESS, implying that the companion does not have an affect on the pulsation in this roAp star. We suggest further photometric observations of this star, and further studies to find more roAp stars in close binaries to characterise how binarity may affect the detection of roAp pulsations.

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Section: Spectroscopymentioning

confidence: 99%

HD 42659: the only known roAp star in a spectroscopic binary observed with B photometry, TESS, and SALT

Holdsworth

Saio

Kurtz

2019

Monthly Notices of the Royal Astronomical Society

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“…A spectroscopic survey of stars classified as helium-rich subdwarfs, especially He-sdB or sdOD using 8m class telescopes has been undertaken. This paper reports an observation of one such star obtained with the high-resolution spectrograph (HRS) on the Southern Africa Large Telescope (SALT) (Buckley et al 2006;Bramall et al 2010;Crause et al 2014) 2 OBSERVATIONS GALEX J184559.8−413827 (α2000 = 18…”

Section: Introductionmentioning

confidence: 99%

GALEX J184559.8−413827: a new extreme helium star identified using SALT★

Jeffery

2017

Monthly Notices of the Royal Astronomical Society

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A high-resolution spectrum of the helium-rich 'hot subdwarf' GALEX J184559.8−413827 ( J1845−4138) obtained with SALT HRS demonstrates it to be the first extreme helium (EHe) star to be discovered in nearly 40 years. A quantitative analysis demonstrates it to have an atmosphere described by T eff = 26 170 ± 750 K, log g/cm s −2 = 4.22 ± 0.10, and a surface chemistry characterised by CNO-processed helium, a 1% contamination of hydrogen (by number), and a metallicity 0.4 dex subsolar. Its distance and position are consistent with membership of the Galactic bulge. Its sharp absorption lines place strong constraints on both the rotation and microturbulent velocities. Spectroscopically, J1845−4138 closely resembles the pulsating EHe star V652 Her, generally considered to be the product of a double helium white dwarf merger evolving to become a helium-rich sdO star.

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“…New observations were obtained with the High Resolution Spectrograph (HRS: R ≈ 43 000, λλ = 4100 − 5200Å Bramall et al 2010) of SALT during 2015 and 2016 on the dates shown in Table 1. The spectra were reduced to order-by-order wavelength calibrated rectified form using the SALT pipeline pyHRS (Crawford et al 2016); orders were stitched into a single spectrum using our own software.…”

Section: Instrumentmentioning

confidence: 99%

SALT revisits DY Cen: a rapidly evolving strontium-rich single helium star

Jeffery

Rao

Lambert

2020

Monthly Notices of the Royal Astronomical Society

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The hydrogen-deficient star DY Cen has been reported as an R CrB-type variable, an extreme helium star (with some hydrogen), and as a single-lined spectroscopic binary. It has been associated with a dramatic change in visual brightness and colour corresponding to a change in effective temperature ( T eff ) of some 20 000 K in the last century. To characterize the binary orbit and T eff changes more precisely, new highresolution spectroscopy has been obtained with SALT. The previous orbital period is not confirmed; previous measurements may have been confused by the presence of pulsations. Including data from earlier epochs (1987, 2002, and 2010), self-consistent spectral analyses from all four epochs demonstrate an increase in T eff from 18 800 to 24 400 K between 1987 and 2015. Line profiles demonstrate that the surface rotation has increased by a factor two over the same interval. This is commensurate with the change in T eff and an overall contraction. Rotation will exceed critical if contraction continues. The 1987 spectrum shows evidence of a very high abundance of the s-process element strontium. The very rapid evolution, non-negligible surface hydrogen and high surface strontium point to a history involving a very late thermal pulse. Observations over the next thirty years should look for a decreasing pulsation period, reactivation of R CrB-type activity as the star seeks to shed angular momentum and increasing illumination by emission lines from nebular material ejected in the past.

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The SALT HRS spectrograph: final design, instrument capabilities, and operational modes

Cited by 56 publications

References 5 publications

HD 42659: the only known roAp star in a spectroscopic binary observed with B photometry, TESS, and SALT

HD 42659: the only known roAp star in a spectroscopic binary observed with B photometry, TESS, and SALT

GALEX J184559.8−413827: a new extreme helium star identified using SALT★

SALT revisits DY Cen: a rapidly evolving strontium-rich single helium star

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