element spots in hgmn stars heidi korhonen centre for star and planet formation & niels bohr...
TRANSCRIPT
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.