Multi-wavelength study of X-ray emitting A- and B-stars

testing the companion hypothesis

Beate StelzerOsservatorio Astronomico di Palermo

N. Huelamo, S. Hubrig (ESO Chile)G. Micela (OA Palermo)

H. Zinnecker (AI Potsdam)E. Guenther (TLS Tautenburg)

X-rays from late-B and early-A type Stars ?

Shock-excited winds

No X-rays

O B A F G K M L

dissipation of magnetic fields

M3A7B5

solar-like -dynamo(in overshoot-layer)

-dynamo ?turb. dynamo ?

fully radiative rad. core + convective envelope fully convective

lg(Lx /Lbol )= -7kT ~ 0.5 keV

lg(Lx /Lbol )= -3....-4kT ~ 1.0 keVRotation-Activity Relation

lg(Lx /Lbol )= -3....-4 ?kT ~ ?Rot.-Act. Relation ?

Dynamo should break down at SpT ~ A7...F3,But X-rays observed from late-B/early-A stars (Caillault & Zoonematkermani 1989, Schmitt et al. 1993, Berghöfer et al. 1996, Hünsch et al. 1998....)

X-rays generated by (unknown) late-type companion stars ???

Testing the companion hypothesis:

Huelamo et al. 2000:X-rays from Lindroos systems

Early-type stars with companionsidentified by their Hardness Ratio ?

WANTED: Stars of early Sp.type (A,B) with companion of late Sp.type (G, K, M)

Lindroos systems (Lindroos 1986)= early-type star with post-TTS companion

X-ray observations with ROSAT:(Schmitt et al 1993; Huelamo et al. 2000)

• companions emit X-rays

• ~ 1/3 of the primaries detected

• many systems not resolvable (ROSAT HRI 5“; ROSAT PSPC 20“)

1. Adaptive Optics observations (Search for cool companions)

2. X-ray follow-up obs. with high spatial resolution (Pinpointing the X-ray source)

3. IR spectroscopy of B/A stars (Search for closer companions)

4. IR spectroscopy of companions (Nature of the companions ?)

Origin of X-rays from intermediate-mass starsObservational Strategy

1. Adaptive Optics observations (Search for cool companions)ADONIS/3.6m ESO

Hubrig et al. (2001) 49 X-ray B-stars 19 companionsHuelamo et al. (2001) 3 X-ray B-stars 1 companionsShatsky & Tokovinin(2002) 115 OB-stars 96 companions

NICS/3.6m TNG,La Palma 3 nights in Aug 03 and Jan 04 (23 A-stars in northern hemisphere)

2. X-ray follow-up obs. with high spatial resolution (Pinpointing the X-ray source)

3. IR spectroscopy of B/A stars (Search for closer companions)

4. IR spectroscopy of companions (Nature of the companions ?)

Origin of X-rays from intermediate-mass starsObservational Strategy

1. Adaptive Optics observations (Search for cool companions)ADONIS/3.6m ESO

Hubrig et al. (2001) 49 X-ray B-stars 19 companionsHuelamo et al. (2001) 3 X-ray B-stars 1 companionsShatsky & Tokovinin(2002) 115 OB-stars 96 companions

NICS/3.6m TNG,La Palma 3 nights in Aug 03 and Jan 04 (23 A-stars in northern hemisphere)

2. X-ray follow-up obs. with high spatial resolution (Pinpointing the X-ray source)Chandra/ACIS: ~ 1“Stelzer et al. 2003, A&A 4075 B-stars + ca. 20 A/B-stars from the Chandra archive

3. IR spectroscopy of B/A stars (Search for closer companions)

4. IR spectroscopy of companions (Nature of the companions ?)

Origin of X-rays from intermediate-mass starsObservational Strategy

1. Adaptive Optics observations (Search for cool companions)ADONIS/3.6m ESO

Hubrig et al. (2001) 49 X-ray B-stars 19 companionsHuelamo et al. (2001) 3 X-ray B-stars 1 companionsShatsky & Tokovinin(2002) 115 OB-stars 96 companions

NICS/3.6m TNG,La Palma 3 nights in Aug 03 and Jan 04 (23 A-stars in northern hemisphere)

2. X-ray follow-up obs. with high spatial resolution (Pinpointing the X-ray source)Chandra/ACIS: ~ 1“Stelzer et al. 2003, A&A 4075 B-stars + ca. 20 A/B-stars from the Chandra archive

3. IR spectroscopy of B/A stars (Search for closer companions)

Pilot study NTT/SofI and 2.2m Calar Alto/MAGIC (PI Huelamo)

4. IR spectroscopy of companions (Nature of the companions ?)

Origin of X-rays from intermediate-mass starsObservational Strategy

1. Adaptive Optics observations (Search for cool companions)ADONIS/3.6m ESO

Hubrig et al. (2001) 49 X-ray B-stars 19 companionsHuelamo et al. (2001) 3 X-ray B-stars 1 companionsShatsky & Tokovinin(2002) 115 OB-stars 96 companions

NICS/3.6m TNG,La Palma 3 nights in Aug 03 and Jan 04 (23 A-stars in northern hemisphere)

2. X-ray follow-up obs. with high spatial resolution (Pinpointing the X-ray source)Chandra/ACIS: ~ 1“Stelzer et al. 2003, A&A 4075 B-stars + ca. 20 A/B-stars from the Chandra archive

3. IR spectroscopy of B/A stars (Search for closer companions)

Pilot study NTT/SofI and 2.2m Calar Alto/MAGIC (PI Huelamo)

4. IR spectroscopy of companions (Nature of the companions ?)proposed for VLT(PI Hubrig)

Origin of X-rays from intermediate-mass starsObservational Strategy

IR and X-ray images of late B-type MS StarsHD 1685

X-rays from A + B Offset X1 – A = 0.1“ Offset X2 – B = 0.1“

ADONIS ESO/3.6m K-band(Hubrig et al. 2001)

Sep. A – B: 2.3“

Chandra ACIS-I(Stelzer et al. 2003)

X-rays from companions B + C

No X-rays from primary A

Result:

Out of 11 systems with B-type MS-primary and IR “companion“ X-rays are detected from

10 (+1?) IR companions, all AO discovered IR objects emit X-rays7 B-Stars even closer companions ? (1 is a SB)

12/15 HAeBe stars detected

ACIS-S

ADONIS

C

A

Huelamo, unpublished

IR and X-ray images of late B-type MS StarsThe Lindroos system HD 113703

X-ray Spectra

simulated Chandrabased on ROSAT parameters

observed Chandra

ROSAT temperature too low, luminosity too high

Spectrum needed to derive plasma properties !

X-ray spectra ofof A/B-stars andof (cool) companionsdifferent ?

Lx / Lbol ratio according to Chandra

Chandra dataof MS B-starsand companions

Upper limitsfor undetected B-starsbelow the value forwind-driven X-rays

Wind-driven stellar X-rays

Chandra dataof MS B-starsand companions

ROSAT dataof MS B-stars(companionsunresolved)

ROSAT: 10 sources

Chandra: 18 sources + 8 upper limits

Wind-driven stellar X-rays

Lx / Lbol ratio according to Chandra

Chandra dataof MS B-starsand companions

ROSAT dataof MS B-stars(companionsunresolved)

Chandra data of HAeBe stars

• Some HAeBe have low-mass companions

• Intermediate Lx/Lbol (uncertain Lbol !)

Wind-driven stellar X-rays

Lx / Lbol ratio according to Chandra

VB

SB

Singles?

Lx / Lbol ratio according to ROSAT

~ 2/3 of O-,B-,A-stars detected in the RASSare binaries !

Lx , Lbol from Berghöfer et al. (1996) and Hünsch et al. (1998)

----A------ ------------B--------------- ----O-----

See Poster E.29 (Schröder & Schmitt)

VB

SB

Singles?

Observed in IRwith AO

23 single A-type starsdetected in the RASSobserved with AO

----A------ ------------B--------------- ----O-----

Lx , Lbol from Berghöfer et al. (1996) and Hünsch et al. (1998)

Lx / Lbol ratio according to ROSAT

IR K-band images of HR7826 (SpT A3 V)

2MASS:Several faint objects within 30“

ghosts

20“

15“

10“

30“

• all 2 MASS sources recovered• further objects within 10“, unidentified in 2MASS

TNG/NICS+AdOpt:Several faint objects within 30“

No reports on binarity.

IR K-band images of HR8307 (SpT A0 V)

TNG/NICS+AdOpt:double source, separation ~ 2“

2MASS:One source at 29“ separation

30“

20“15“

10“

• 83 pc• lgLx = 30.6 (RASS; Huensch et al. 1998)

• no companion detected in Speckle survey (McAlister et al. 1987)

at detectable separation of 0.61“....1.36“ depending on P.A.

IR spectrum of HD 32964HD 32964A SB: 2 components of ~2.4 Msun eachHD 32964B Lindroos companion at 53“ (K5 V; probably unrelated)HD 32964C Adaptive Optics companion at 1.6“The only Chandra X-ray source is HD32964 C.

IR spectrum of HD 32964

Comparison Spectra:

Spectrum of the Adaptive Optics companion HD32964C.

HD 32964A SB: 2 components of ~2.4 Msun eachHD 32964B Lindroos companion at 53“ (K5 V; probably unrelated)HD 32964C Adaptive Optics companion at 1.6“The only Chandra X-ray source is HD32964 C.

IR CMD for „Companions“

Chandra sample

11 MS stars have15 „companions“ (12 X-ray detected)

15 HAeBe stars have9 „companions“(4 X-ray detected)

„Companions“ with ........no J-mag 7....not on PMS 5....likely on PMS12

Baraffe et al. (1998)

Undetected in X-raysDetected in X-rays

1. Adaptive Optics observations: ADONIS/3.6m ESO

Hubrig et al. (2001) 40 % of X-ray B-stars have companions

at 0.2-14“NICS/3.6m TNG,La Palma

data in analysis several new objects in 23 X-ray A-stars

2. X-ray follow-up observations of AO targets:Chandra ACIS

7(11) B-stars emit X-rays;X-ray properties similar to AO

companions sub-arcsecond

companions ?

3. IR spectroscopy of Chandra-detected B/A stars Pilot studies underway (NTT and Tautenburg):

AO companions rediscovered;observations need careful setup

Summary