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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

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Element spots in hgmn stars

Element spots in HgMn stars

Heidi Korhonen

Centre for Star and Planet Formation

&

Niels Bohr Institute

University of Copenhagen


Outline
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
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)


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


Vertical stratification
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



Indications of spots on hgmn star and
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 and
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


More spotted hgmn stars
More spotted HgMn stars

Kochukhov et al. 2005

μ Lep: Kochukhov et al. 2011

AR Aur: Hubrig et al. 2006


Mapping chemical spots
Mapping chemical spots

From O. Kochukhov


First spot map hg in and
First spot map: Hg in α And

Adelman et al. 2002


Configurations of chemical spots 66 eria
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),


Configurations of chemical spots hd11753 or phe
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


Weather in andromedae
“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
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


Long term observations of hd11753
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


Equivalent widths at different epochs
Equivalent Widths at different epochs

Korhonen 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

Oct 2000

Oct part1

  • First discoveredbyBriquet et al. (2010)

  • Reliabilitystudied in moredetailbyKorhonen et al. (2013)

Oct part 2

Dec 2000

Korhonen et al. 2013


Magnetic fields in hgmn stars
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


Correlation of the magnetic field and spots
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


Conclusions
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.


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