Observations of non-magnetic CP stars

IAU Symposium No. 224 The A-Star Puzzle

Observations of non-magnetic

CP stars

Glenn M. Wahlgren

Lund Observatory


HgMn -- hot Am -- Am

He-weak

He-strong Bp Ap

B2 B5 B7 B9.5/A0 A2/A3


AmHot Am

HgMnHe-w

ApBpBp Ap


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


New wavelength regime : far ultraviolet (FUSE)

HD 108662 Bp

HD 182308 B9p HgMn

HD 36981 B5 V



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


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.


Elemental abundance distribution for Lupi A (HgMn)

The heaviest stable elements ( 73 < Z < 83 )

(But what does this mean ?)

_ _


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


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


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


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)


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)


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))


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)


Crossing Boundaries: HgMn – Am stars

figures from Dolk (2002, PhD Thesis)

Deficiency for all Teff

Ex: He, C, N, O

Enhancement for all Teff

Ex: Nd, Pr, Ce, Ba, Sr, (V, Fe)



figures from Dolk (2002, PhD thesis)

Trend for abundance to decrease as Teff decreases

Ex: Ni, Al, S

Trend for abundance to increase as Teff increases

Ex: Mn, P, Ca, Sc, Ti, Y, Zr



figure from Adelman et al. (2003)

X - HgMn O - Am

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Observations of non-magnetic CP stars