SALT spectroscopy of hydrogen-deﬁcient stars Simon JEFFERY1,2 and Brent MISZALSKI3,4 1Armagh Observatory and Planetarium, 2Trinity College Dublin, 3Southern Africa Large Telescope, 4South African Astronomical Observatory Summary. The majority of hot subdwarfs lie on or close to the helium main-sequence. Many have hydrogen-rich surfaces, but a substantial fraction have hydrogen-depleted or hydrogen-deﬁcient surfaces. Amongst the former, three were known to show extraordinary overabundances of heavy elements including zirconium and lead. A limited survey with Subaru/HDS revealed three new lead-rich subdwarfs. A much wider survey is in progress using SALT. Discoveries include two new extreme helium stars, new intermediate helium subdwarfs, and a new lead star. Analysis of the growing sample shows evidence of connections between hydrogen-deﬁcient classes. Introduction The majority of hot subdwarfs are hydrogen-rich, with helium strongly suppressed. However, some 10% show helium enrich- ments from near equity with hydrogen up to nearly pure helium surfaces (Geier 2013). This diversity is apparent in the helium sub- classes identiﬁed by Drilling et al. (2013), who also noted that cer- tain classes of helium-rich hot subdwarf and extreme helium stars are diﬃcult to distinguish at low resolution. At high resolution, more exotic chemistries were discovered by Naslim et al. (2011, 2013), including zirconium- and lead-rich subdwarfs. The extreme rarity of these stars demands a search for additional specimens. We describe a survey using the Southern African Large Telescope (SALT) to identify extreme helium stars and exotic chemistry sub- dwarfs, and to map their connections. Figure 1: SALT/HRS atlas of early-type helium-rich hot subdwarfs binned to show major hydrogen and helium lines. Rest locations of principal hydrogen, helium and carbon lines are indicated in colour . Figure 2: As Fig. 1: late type spectra. Observations SALT/HRS From 2016 to 2018, observations have been ob- tained with the SALT High Resolution Spectrograph (HRS) for southern helium-rich subdwarfs and other stars identiﬁed from low-resolution surveys. Echelle spectra were reduced, blaze cor- rected, resampled and stitched (Figs. 1 and 2). SALT/RSS Commencing 2018, observations have been ob- tained with the SALT Robert Stobie Spectrograph (RSS) (Figs. 4 and 5). Methods Classiﬁcation using the Drilling et al. (2013) system gives prox- ies for eﬀective temperature Teﬀ, surface gravity g, and helium abundance (He/H). The object is to identify stars of interest, es- pecially in the cool low-gravity domain. More reﬁned measure- ments are obtained by ﬁtting the observed spectra in a three- dimensional model grid covering the same parameters. The grid must be adapted (and iterated) to match the heavy-element dis- tribution since this strongly inﬂuences the atmosphere structure at low hydrogen abundances. Once established (and then ﬁxed), a ﬁnal model atmosphere is computed and elemental abundances of minor species are measured. Fig. 3 shows selected results. Figure 3: Surface properties of selected SALT subdwarfs (red), compared with extreme helium stars (black squares), extreme helium subdwarfs (black diamonds) and intermediate helium subdwarfs (violet diamonds). The Eddington limit (Thomson scattering: dashed), luminosity-to-mass contours (solar units: dotted), the post-merger track for a 0.30+0.25 M⊙ He+He white dwarf merger (Zhang & Jeﬀery 2012) (maroon), and the post-ﬂash track of a 0.46921 M⊙’late hot ﬂasher’ (metallicity Z = 0.01) (Miller Bertolami et al. 2008) (orange) are also shown. Highlights J18455−4138. Originally classiﬁed as a helium-rich subdwarf, raw HRS data indicated a prominent spectrum of strong sharp lines found to be mostly singly-ionized nitrogen. The Balmer lines are negligible, and He ii 4686 is much weaker than in other He-rich subdwarfs. Bearing a strong similarity to V652 Her, ﬁne analysis demonstrated that J18455−4138 is a relatively high-gravity