Element spots in HgMn stars

1. Element spots in HgMn stars Heidi Korhonen Centre for Star and Planet Formation & Niels Bohr Institute University of Copenhagen

2. Outline • General properties of HgMn stars • Some history of line profile variability detections • Chemical element surface configurations • Temporal evolution of chemical spots • Are HgMn stars magnetic? Kochukhov et al. 2005

3. HgMn stars • Late B-type stars • Extreme overabundance of Hg/Mn (not always Mn) • Slowly rotating: <v sin i>=29 km/s • No strong large-scale organized magnetic fields • No enhancement in Rare Earth Elements, but of heavy elements W, Re, Os, Ir, Pt, Au, Hg, Tl, Pb, Bi • Anomalous isotopic abundances of He, Hg, Pt, Tl, Pb, Ca. • About 150 stars are known Dolk et al. 2002 Ca-48 shift in HD 175640 (HR 7143) Castelli & Hubrig (2004)

4. Multiplicity among HgMn stars • Observations of 57 HgMn stars with NACO @ VLT • 25 binaries, • 3 triples, • 1 quadruple • Nine companion candidates found for the first time • Only five stars in the sample show no indication of multiplicity, taking into account that 44 systems are confirmed or suspected spectroscopic binaries Schöller et al 2010

5. Vertical stratification HD 178065 • Some evidence for vertical stratification: • ofCr (Savanov & Hubrig 2001) • of Mn (Alecian 1982; Sigut2001) • of Ga(Lanz et al. 1993) • FromtheThiam et al. (2010) sample offour HgMn stars only HD 178065 shows stratification of Mn • Dubaj et al. (2004) found no conclusive evidence of stratification of Fe lines in HD 143807A. • Makaganiuk et al. (2012) found no convincing evidence of vertical stratification of Ti and Y in HD11753 Ti Cr Mn Thiam et al. 2010 Fe

6. From Kurtz & Martinez 2000

7. Indications of spots on HgMn star: α And • Ryabchikova et al. (1999) did chemical abundance analysis of α And • They discovered changing line profiles of Hg at 3983 Å. • But they only had three epochs of observations.

8. Detection of spots on HgMn star: α And „This first definitively identified spectrum variation in any mercury-manganese star is not due to the orbital motion of the companion. Rather, the variation is produced by the combination of the 2.38236 day period of rotation of the primary that we determined and a nonuniform surface distribution of mercury that is concentrated in its equatorial region.“ (Adelman et al. 2002) Wade et al. 2006 Adelman et al. 2002

9. More spotted HgMn stars Kochukhov et al. 2005 μ Lep: Kochukhov et al. 2011 AR Aur: Hubrig et al. 2006

10. Mapping chemical spots From O. Kochukhov

11. First spot map: Hg in α And Adelman et al. 2002

12. Configurationsofchemicalspots: 66 EriA • General asymmetry of chemical composition for the two hemispheres. • All four studied elements show higher abundance at rotational phases from 0.5 – 0.1 and a lower abundance for phases 0.1–0.5. Makaganiuk et al. 2011a A relative element underabundance on the side facing the secondary has also been reported for Y in AR Aur A (Hubrig et al. 2006),

13. Configurationsofchemicalspots: HD11753 (orφPhe) Y shows the largest variability Sr concentrates in one spot Ti has the largest area covered by spots Cr shows the smallest variability Makaganiuk et al. 2012

14. “Weather” in α Andromedae • Slow variations in the chemical structures of HgMn star α And are seen from maps spanning seven years • Kochukhov et al. (2007) explained the behaviour with a non-equilibrium, dynamical evolution of the heavy-element clouds created by atomic diffusion. • Possibly the same underlying physics as the weather patterns on terrestrial and giant planets Kochukhov et al. 2007

15. Secularspotevolutionis also seen in AR Aur Epochs of observations black diamonds: 2002 blue crosses: 2005 green circles: 2008 All observations from phase ~0.80 Hubrig et al. 2010

16. Long-term observations of HD11753 YII SrII Oct 2000 Dec 2000 Aug 2009 Jan 2010 Korhonen et al. 2013 All the data from CORALIE spectrograph at La Silla

17. Equivalent Widths at different epochs Korhonen et al. 2013 Oct 2000 (plus), Dec 2000 (asterisk), Aug 2009 (square), Jan 2010 (triangle)

18. Fast temporal evolution of spots in HD11753 Oct 2000 Oct part1 • First discoveredbyBriquet et al. (2010) • Reliabilitystudied in moredetailbyKorhonen et al. (2013) Oct part 2 Dec 2000 Korhonen et al. 2013

19. Magnetic fields in HgMn stars? • Detectionsofmagneticfields in someHgMnstarshavebeenreported: • e.g., Mathys & Hubrig 1995; Hubrig & Castelli 2001; Hubrig et al. 2006 • Other studies on the other hand have not found magnetic fields: • e.g., Landstreet 1982; Shorlinet al. 2002; Wade et al. 2006; Makaganiuk et al. 2011 • At times the results agree, e.g., the non-detection of magnetic field in HD 71066 (Hubrig et al. 1999, Hubrig et al. 2006; Kochukhov et al. 2013) • At times the the results do not agree, e.g., in AR AurHubrig et al. (2010) detect weak field and Folsom et al. (2010) do not. • In the cases of discrepancy most of the non-detections are using LSD method, and the detections using the moment technique. HD 71066 Kochukhov et al. 2013

20. Correlation of the magnetic field and spots? HD 11753 Korhonen et al. 2013 NOTE: Investigations using LSD method have not found magnetic fields in HD 11753 (Makaganiuk et al. 2012; Kochukhov et al. 2013) Hubrig et al. 2012

21. Conclusions • HgMn stars are usually part of a binary or multiple system • Many of them show line-profile variations caused by chemical spots, most often in Hg and Mn, but also in other elements, e.g., Y, Sr, Ti, Cr and Ba • Secular spot evolution was discovered by Kochukhov et al. (2007) • Fast spot evolution by Briquet et al. (2010) • Weak magnetic fields have been reported in some HgMn stars • More detailed studies of magnetic fields using high resolution, high signal-to-noise spectropolarimetric observations are needed to resolve the issue concerning magnetic field detections.