1. IAU Symposium No. 224 The A-Star Puzzle Observations of non-magnetic CP stars Glenn M. Wahlgren Lund Observatory

2. IAU Symposium No. 224 The A-Star Puzzle HgMn -- hot Am -- Am He-weak He-strong Bp Ap B2 B5 B7 B9.5/A0 A2/A3

3. IAU Symposium No. 224 The A-Star Puzzle Am Hot Am HgMn He-w Ap Bp Ap

4. IAU Symposium No. 224 The A-Star Puzzle Topics in nmCP star research – One Decade Ago Basic properties (colors, fluxes, temperatures, classification) Binarity (statistics) Spectrum analysis (element abundances, isotopes) Extensions to UV (IUE, HST) Rumblings about stratification Magnetic fields (presence in nmCP stars) Variability (photometric, spectroscopic) New wavelength regimes X-ray: late-type B stars

5. IAU Symposium No. 224 The A-Star Puzzle New wavelength regime : far ultraviolet (FUSE) HD 108662 Bp HD 182308 B9p HgMn HD 36981 B5 V

6. IAU Symposium No. 224 The A-Star Puzzle

7. Binarity / multiplicity among nmCP stars Companions continue to be identified, > 60% (Hubrig & Mathys 1996) HgMn stars have a high presence in SB2 systems Am stars have a high presence in binaries Companions with Teff < 10000K are Am stars (?)(Ryabchikova et al. 1998) Main sequence B, A stars as companions to Cepheids (Evans 1995), with implications for ages and onset of CP phenomenon SU Cyg system: A (Cepheid) + (B (HgMn) +C), Orb. Per. 549.16, 4.67 d (Wahlgren & Evans 1998) T Mon system: A (Cepheid) + (B(Bp) + C), C implied from velocities (Evans et al. 1999) AW Per system: A (Cepheid) + (B(B8V) +C), C implied from mass function (Evans et al. 2000) X-rays appear to originate from cool companions of late-B stars

8. IAU Symposium No. 224 The A-Star Puzzle Elemental abundances Categories of abundance analyses: Am stars: Studies favor the observation of stellar clusters for determining the onset and development of peculiarity with age. The basic picture of the Am abundance pattern has not changed. HgMn stars: Studies focus on individual stars for specific tasks, such as isotope analysis, the study of a specific element(s) in several stars, or the abundance distribution of a particular star. Progress has been made in including more elements into the abundance pattern and in identifying new phenomena from the spectra.

9. IAU Symposium No. 224 The A-Star Puzzle Elemental abundance distribution for  Lupi A (HgMn) The heaviest stable elements ( 73 < Z < 83 ) (But what does this mean ?) __

10. IAU Symposium No. 224 The A-Star Puzzle Abundance analyses: lessons learned The influence of velocity fields on line profiles. a)Am stars: strong lines show asymmetry, with deeper blue line wings (Landstreet 1998). b)HgMn stars: turbulent velocity influences both the derived abundance and isotope composition of Hg in sharp-lined stars (Dolk et al. 2003). figure from Landstreet (1998) A1m V A0 IV B9 HgMn B9.5 V B9 HgMn A1m V A2m A5m

11. IAU Symposium No. 224 The A-Star Puzzle Isotope anomalies Previous knowledge pertained to He, Pt, Hg New observations extended to include: Ca (Castelli & Hubrig 2004) wavelength shifts of Ca II IR triplet interpreted as anomalous isotope composition in HgMn stars Ga (Nielsen et al. 2000, & PhD thesis 2002) mention of possible wavelength shift of Ga II lines in HgMn star  Cancri Pt (several studies of HgMn stars) variability among lines Hg (several studies of HgMn stars) q-parameter found to be untenable at high spectral resolution heaviest isotopes most prominent isotopic composition not a constant for different lines of Hg II Pb (Leckrone et al. 1999) tentative claim to an anomaly, based on one Pb III line in HgMn star  Lupi. Tl (Leckrone et al. 1996) wavelength shift of Tl II 1908Å indicative of only heavier isotope present in HgMn star  Lupi

12. IAU Symposium No. 224 The A-Star Puzzle Weak emission lines in the He-weak star 3 Cen A Multiplet 13 Multiplet 11 WEL first detected in CP stars 3 Cen A (He-w) and 46 Aql (HgMn) (Sigut et al. 2000). Later expanded to identify 350 lines in 3 Cen A (Wahlgren & Hubrig 2004). Lines identified originate from high- excitation energy levels in singly- ionized atoms. Elements identified: P, Si, Ca, Cr, Mn, Fe, Co, Ni, Cu, Hg

13. IAU Symposium No. 224 The A-Star Puzzle Weak emission lines in HgMn stars Mn-rich Mn-normal WEL present in all main sequence mid to late B stars. Implications for element segregation in upper atmosphere. (Wahlgren & Hubrig 2000)

14. IAU Symposium No. 224 The A-Star Puzzle Spectrum variability of the HgMn star  And Hg II 3984Å line shows continuous variations with a period of 2.38 d (rotation). Less pronounced variability detected in lines Hg II 6149, 5677, as well as other lines, but need to be addressed in terms of binary component (96.88 d period). DI techniques show that the line profile variability can be explained as an inhomogeneous distribution of mercury, with higher concentrations occurring along the rotational equator. Does the Hg surface distribution have a magnetic origin ??? Adelman et al. (2002) Ilyin (2000) Ryabchikova et al. (1999) Wahlgren et al. (2002)

15. IAU Symposium No. 224 The A-Star Puzzle Magnetic fields in nmCP stars The potential for complex magnetic fields has been suggested through observations of the desaturation of magnetically sensitive line pairs in HgMn and Am stars. Mathys & Lanz (1990): o Peg (A1m) Lanz & Mathys (1993): HD 29173 (Am), HD195479A (Am) Mathys & Hubrig (1995): 74 Aqr A (HgMn),  Lupi B (A2m) Hubrig et al. (1999, 2001): several HgMn stars Also, see catalogue of Bychkov et al. (2003). However, no fields are detected via the longitudinal Zeeman effect, implying no field structures similar to magnetic Ap stars. (Shorlin et al. 2002). But can there be other evidence ? (abundances of certain ions (Pr III))

16. IAU Symposium No. 224 The A-Star Puzzle Stratification in HgMn stars Stratification has been suggested based upon: -Ionization anomalies -Abundance trends of Cr II lines in the wing of H  - He line profiles Concerns: -Treatment of depth dependent turbulence -Mixing data of different quality (ex. IUE and optical) figure from Nielsen (2002)

17. IAU Symposium No. 224 The A-Star Puzzle Crossing Boundaries: HgMn – Am stars figures from Dolk (2002, PhD Thesis) Deficiency for all T eff Ex: He, C, N, O Enhancement for all T eff Ex: Nd, Pr, Ce, Ba, Sr, (V, Fe)

18. IAU Symposium No. 224 The A-Star Puzzle Crossing Boundaries: HgMn – Am stars figures from Dolk (2002, PhD thesis) Trend for abundance to decrease as T eff decreases Ex: Ni, Al, S Trend for abundance to increase as T eff increases Ex: Mn, P, Ca, Sc, Ti, Y, Zr

19. IAU Symposium No. 224 The A-Star Puzzle Crossing Boundaries: HgMn – Am stars figure from Adelman et al. (2003) X - HgMn O - Am