SALT spectroscopy of hydrogen-deficient 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 . 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 . Analysis of the growing sample shows evidence of connections between hydrogen-deficient classes.

Introduction Observations References

The majority of hot subdwarfs are hydrogen-rich, with helium SALT/HRS From 2016 to 2018, observations have been ob- Ahmad A., & Jeffery C. S., 2003, A&A, 402, 335 strongly suppressed. However, some 10% show helium enrich- tained with the SALT High Resolution Spectrograph (HRS) for Beli´ere,E. P., 2018, BSc Project, Trinity College Dublin ments from near equity with hydrogen up to nearly pure helium southern helium-rich subdwarfs and other stars identified from Drilling J. S., et al. 2013, A&A, 551, A31 surfaces (Geier 2013). This diversity is apparent in the helium sub- low-resolution surveys. Echelle spectra were reduced, blaze cor- Geier S., 2013, A&A, 549, A110 classes identified by Drilling et al. (2013), who also noted that cer- rected, resampled and stitched (Figs. 1 and 2). Jeffery C. S., 2017, MNRAS, 470, 3557 tain classes of helium-rich hot and extreme helium stars Jeffery C. S., 1998, MNRAS, 294, 391 are difficult to distinguish at low resolution. At high resolution, Miller Bertolami M. M., et al. 2008, A&A, 491, 253 SALT/RSS Commencing 2018, observations have been ob- more exotic chemistries were discovered by Naslim et al. (2011, Moehler S., et al. 1990b, A&A, 86, 53 tained with the SALT Robert Stobie Spectrograph (RSS) (Figs. 2013), including zirconium- and lead-rich subdwarfs. The extreme Naslim N., et al. 2011, MNRAS, 412, 363 4 and 5). rarity of these stars demands a search for additional specimens. Naslim N., et al. 2013, MNRAS, 434, 1920 We describe a survey using the Southern African Large Telescope Zhang X., Jeffery C. S., 2012, MNRAS, 419, 452 (SALT) to identify extreme helium stars and exotic chemistry sub- dwarfs, and to map their connections. Methods Classification using the Drilling et al. (2013) system gives prox- ies for effective temperature Teff, surface 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), -to-mass contours (solar units: dotted), the post-merger track for a 0.30+0.25 M He+He merger (Zhang & Jeffery 2012) (maroon), and the post-flash track of a 0.46921 M ’late hot flasher’ ( Z = 0.01) (Miller Bertolami et al. 2008) (orange) are also shown.

Figure 4: SALT/RSS atlas of hydrogen-deficient subdwarfs and related stars, including pro- Figure 1: SALT/HRS atlas of early-type helium-rich hot subdwarfs binned to show major visional spectral types. The lowest four spectra may be white dwarfs. Stars also observed with hydrogen and helium lines. Rest locations of principal hydrogen, helium and carbon lines are Highlights HRS are labelled ’+hrs’ indicated in colour . 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 ex- −2 treme helium star with Teff = 26 170 ± 750 K, log g/cm s = 4.22 ± 0.10 and a surface characterized by CNO-processed helium with a 1% contamination from hydrogen (Jeffery 2017) (Fig. 3).

J19376−4303. The raw HRS spectrum appeared similar to that of J18455−4138. The reduced spectrum reveals stronger Balmer lines, indicating hydrogen and helium abundances of 76% −2 and 33% respectively. With Teff ≈ 24 200 K and log g/cm s ≈ 4.2 ± 0.10, J19376−4303 lies close to the , with only moderate helium enhancement and relatively normal CNO abundances. These provisional results await confirmation.

J19108−4417. The HRS spectrum resembles extreme he- ◦ lium star LS IV+6 2 (Jeffery 1998). A quick look gave Teff ≈ 35 600 K and log g/cm s−2 ≈ 5.0, but a second look led to −2 Teff ≈ 32 000 K and log g/cm s ≈ 4.2 ± 0.10, and indeed similar to LS IV+6◦2 (Beli´ere 2018). The discrepancy high- lights difficulties with analysing SALT/HRS spectra, which will be partly addressed using data from SALT/RSS. The exercise showed helium-rich subdwarfs PG 1415+492 (Ahmad & Jeffery 2003) and PG 0135+243 (Moehler et al. 1990) also have Teff and g similar to LS IV+6◦2; the connections are much closer than hitherto realised.

EC19529−4430. The RSS spectrum of this high proper- motion star shows no ionized helium lines and Balmer lines much weaker than the neutral helium lines, similar in many respects to J18455−4138. A defining characteristic is weakness of all metal Figure 5: As Fig. 4, but including several intermediate helium-rich cases. The bottom Figure 2: As Fig. 1: late type spectra. lines. spectrum is a post-AGB star.