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

Element spots in HgMn stars

Heidi Korhonen

Centre for Star and Planet Formation&

Niels Bohr Institute

University of Copenhagen

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

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)

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

Multiplicity among HgMn stars

Schöller et al 2010

Vertical stratification

• Some evidence for vertical stratification:– of Cr (Savanov & Hubrig 2001)– of Mn (Alecian 1982; Sigut 2001) – of Ga (Lanz et al. 1993)

• From the Thiam et al. (2010) sample of four 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

Thi

am e

t al

. 20

10

HD 178065

Ti

Cr

Mn

Fe

From Kurtz & Martinez 2000

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.

Detection of spots on HgMn star: α And

Wade et al. 2006

„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)

Ade

lman

et

al.

2002

More spotted HgMn stars

AR Aur: Hubrig et al. 2006

Kochukhov et al. 2005 μ Lep: Kochukhov et al. 2011

Map

ping

che

mic

al s

pots

From O. Kochukhov

First spot map: Hg in α And

Adelman et al. 2002

Configurations of chemical spots: 66 EriA

Makaganiuk et al. 2011a

• 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.

A relative element underabundance on the side facing the secondary has also been reported for Y in AR Aur A (Hubrig et al. 2006),

Configurations of chemical spots: HD11753 (or φ Phe)

Makaganiuk et al. 2012

Ti has the largest area covered by spots

Sr concentrates in one spot

Y shows the largest variability

Cr shows the smallest variability

“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

Secular spot evolution is also seen in AR Aur

Epochs of observationsblack diamonds: 2002blue crosses: 2005green circles: 2008

All observations from phase ~0.80

Hubrig et al. 2010

Long-term observations of HD11753 O

ct

2000

Dec

200

0A

ug

200

9Ja

n 2

010

Korhonen et al. 2013

YII SrII

All the data from CORALIE spectrograph at La Silla

Equivalent Widths at different epochs

Kor

hone

n et

al.

2013

Oct 2000 (plus), Dec 2000 (asterisk), Aug 2009 (square), Jan 2010 (triangle)

Fast temporal evolution of spots

in HD11753

Fast temporal evolution of spots

in HD11753

• First discovered by Briquet et al. (2010)

• Reliability studied in more detail by Korhonen et al. (2013)

Korhonen et al. 2013

Oct 2000

Dec 2000

Oct part1

Oct part 2

Magnetic fields in HgMn stars?

• Detections of magnetic fields in some HgMn stars have been reported:– 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; Shorlin et 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 Aur Hubrig 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. Kochukhov et al. 2013

HD 71066

Correlation of the magnetic field and spots?

Kor

hone

n et

al.

2013

Hubrig et al. 2012

NOTE: Investigations using LSD method have not found magnetic fields in HD 11753 (Makaganiuk et al. 2012; Kochukhov et al. 2013)

HD 11753

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.